​MN 63 Culamalunkya Sutta: The Shorter Discourse to Malunkyaputta 

Thus have i heard. 

On one occasion the Blessed One was living at Savatthi in Jeta's Grove, Anathapindika's Park. While venerable Malunkyaputta was alone in meditation, the following thought arose in his mind: "These speculative views have been undeclared by the Blessed One, set aside and rejected by him, namely: 'the world is eternal' and 'the world is not eternal'; 'the world is finite' and 'the world is infinite'; 'the soul is the same as the body' and 'the soul is one thing and the body another'; and 'after death a Tathagata exists' and 'after death a Tathagata does not exist' and 'after death a Tathagata both exists and does not exist' and 'after death a Tathagata neither exists nor does not exist.' 

The Blessed One does not declare these to me, and I do not approve of and accept the fact that he does not declare these to me, so I shall go to the Blessed One and ask him the meaning of this. If he declares to me either 'the world is eternal' or 'the world is not eternal'...or 'after death a Tathagata neither exists nor does not exist,' then I will lead the holy life under him; if he does not declare these to me, then I will abandon the training and return to the low life."

Then in the evening, Venerable Malunkyaputta rose from meditation and went to the Blessed One. After paying homage to him, he sat down at one side and told him: "Here, venerable sir, while I was alone in meditation, the following thought arose in my mind: 'These speculative views have been undeclared by the Blessed One...If he does not declare these to me, then I will abandon the training and return to the low life.' If the Blessed One knows 'the world is eternal' let the Blessed One declare to me 'the world is eternal'; if the ​Blessed One knows 'the world is not eternal' let the Blessed One declare to me 'the world is not eternal.' If the Blessed One does not know either 'the world is eternal' or 'the world is not eternal' then it is straightforward for one who does not know and does not see to say: 'I do not know, I do not see.' 

Malunkyaputta: "If the Blessed One knows 'the world is finite'...'the world is infinite'...'the soul is the same as the body'...'the soul is one thing and the body another'...'after death a Tathagata exists' ...'after death a Tathagata does not exist'...If the Blessed One knows 'after death a Tathagata both exists and does not exist' let the Blessed One declare that to me; if the Blessed One knows 'after death a Tathagata neither exists nor does not exist' let the Blessed One declare that to me. If the Blessed One does not know either 'after death a Tathagata both exists and does not exist' or 'after death a Tathagata neither exists nor does not exist' then it is straightforward for one who does not know and does not see to say: 'I do not know, I do not see.'"

Buddha :"How then, Malunkyaputta, did I ever say to you: 'Come, Malunkyaputta, lead the holy life under me and I will declare to you "the world is eternal"...or "after death a Tathagata neither exists nor does not exist'"?"
Malunkyaputta: "No, venerable sir."
Buddha: "Did you ever tell me: 'I will lead the holy life under the Blessed One, and the Blessed One will declare to me "the world is eternal"...or "after death a Tathagata neither exists nor does not exist'"?"
Malunkyaputta: "No, venerable sir."
Buddha: "That being so, misguided man, who are you and what are you abandoning? "If anyone should say thus: 'I will not lead the holy life under the Blessed One until the Blessed One declares to me "the world is eternal"...or "after death a Tathagata neither exists nor does not exist'" that would still remain undeclared by the Tathagata and meanwhile that person would die. Suppose Malunkyaputta, a man were wounded by an arrow thickly smeared with poison, and his friends and companions, his kinsmen and relatives, brought a surgeon to treat him. The man would say: I will not let the surgeon pull out this arrow until I know whether the man who wounded me was a noble or a brahmin or a merchant or a worker... until I know the name and clan of the man who wounded me...until I know whether the man who wounded me was tall or short or of middle height... until I know whether the man who wounded me was dark or brown or golden-skinned...until I know whether the man who wounded me lives in such a village or town or city...until I know whether the bow that wounded me was a long bow or a crossbow...until I know whether the bowstring that wounded me was fiber or reed or sinew or hemp or bark...until I know whether the shaft that wounded me was wild or cultivated... until I know with what kind of feathers the shaft that wounded me was fitted - whether those of a vulture or a crow or a hawk or a peacock or a stork;...until I know with what kind of sinew the shaft that wounded me was bound - whether that of an ox or a buffalo or a lion or a monkey;...until I know what kind of arrow it was that wounded me - whether it was hoof-tipped or curved or barbed or calf-toothed or oleander.'"

​"All this would still not be known to that man and he would die due to the delay in treatment in his quest to answer his questions. So too, Malunkyaputta, if anyone should say thus: 'I will not lead the holy life under the Blessed One until the Blessed One declares to me: "the world is eternal"...or "after death a Tathagata neither exists nor does not exist" that would still remain undeclared by the Tathagata and meanwhile that person would die. "

"Malunkyaputta, if there is the view 'the world is eternal' the holy life cannot be lived; and if there is the view 'the world is not eternal' the holy life cannot be lived. Whether there is the view 'the world is eternal' or the view 'the world is not eternal' there is birth, there is ageing, there is death, there are sorrow, lamentation, pain, grief, and despair, the destruction of which I prescribe here and now. "

"If there is the view 'the world is finite'...'the world is infinite'.. .'the soul is the same as the bod'...'the soul is one thing and the body another'...'after death a Tathagata exists'...'after death a Tathagata does not exist' the holy life cannot be lived...If there is the view 'after death a Tathagata both exists and does not exist' the holy life cannot be lived; and if there is the view 'after death a Tathagata neither exists nor does not exist' the holy life cannot be lived. Whether there is the view 'after death a Tathagata both exists and does not exist' or the view 'after death a Tathagata neither exists nor does not exist' there is birth, there is ageing, there is death, there are sorrow, lamentation, pain, grief, and despair, the destruction of which I prescribe here and now. "
(Even if one were to debate non-stop on the assumptions on world eternity, existence of soul and so on; one cannot deny the first noble truth - there is suffering still exists and holds true. One should focus on the noble truths instead of endless non-beneficial debates)

 "Therefore, Malunkyaputta, remember what I have left undeclared as undeclared, and remember what I have declared as declared. And what have I left undeclared- 10?
- 'The world is eternal' -
- 'The world is not eternal'
- 'The world is finite'
- 'The world is infinite' 
- 'The soul is the same as the body'
- 'The soul is one thing and the body another'
-'After death a Tathagata exists' -
- 'After death a Tathagata does not exist'
- 'After death a Tathagata both exists and does not exist'
- 'After death a Tathagata neither exists nor does not exist'
"Why have I left all the above undeclared? Because it is un-beneficial, it does not belong to the fundamentals of the holy life, it does not lead to disenchantment, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbana. That is why I have left it undeclared.

"And what have I declared?
- 'This is suffering'
- 'This is the origin of suffering'
- 'This is the cessation of suffering'
- 'This is the way leading to the cessation of .suffering'
Why have I declared that- the four noble truths? Because it is beneficial, it belongs to the fundamentals of the holy life, it leads to disenchantment, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbana. That is why I have declared it. "

"Therefore, Malunkyaputta, remember what I have left undeclared as undeclared, and remember what I have declared as declared." 
​
That is what the Blessed One said. The venerable Malunkyaputta was satisfied and delighted in the Blessed One's words. 

In summary, Malunkyaputta was dissatisfied that the Buddha has not answered 10 questions concerning existence and non-existence (whether or not the world is eternal, whether or not the world if finite or infinite or whether or not the self and the body are one thing or different things, or in what way the arahant manifests after death). Thus he confronted the Buddha to asked why he did not answer those questions. With the simile of the man struck by a poisoned arrow, the Buddha makes plain exactly what he does and does not teach. ​He explained to Malunkyaputta that these questions are not expounded upon because they are not relevant and not beneficial and does not lead one to the goal of ending suffering. Instead he should focus on what the Buddha had declared - the four noble truths that will lead to liberation, nibbana. 

References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The middle length discourses of the Buddha (Bhikkhu Bodhi)