​MN 151 Pindapataparisuddhi Sutta: The Purification of Almsfood 

Thus have i heard. 

On one occasion the Blessed One was living at Rajagaha in the Bamboo Grove, the Squirrels' Sanctuary. Then in the evening, venerable Sariputta rose from meditation and went to the Blessed One. After paying homage to him, he sat down at one side. The Blessed One then said to him: "Sariputta, your faculties are clear. The color of your skin is pure and bright. What abiding do you often abide in now, Sariputta?"

Sariputta: "Now, venerable sir, I often abide in voidness."
Buddha: "Good, good, Sariputta! Now, indeed, you often abide in the abiding of a great man. For this is the abiding of a great man, namely, voidness. So, Sariputta, if a bhikkhu should wish: 'May I now often abide in voidness,' he should consider thus: 'On the path by which I went to the village for alms, or in the place where I wandered for alms, or on the path by which I returned from the alms round, was there any desire, lust, hate, delusion, or aversion in my mind regarding forms cognizable by the eye?'"

" If, by so reviewing, he knows thus: 'On the path by which I went to the village for alms, or in the place where I wandered for alms, or on the path by which I returned from the alms round, there was desire, lust, hate, delusion, or aversion in my mind regarding forms cognizable by the eye,' then he should make an effort to abandon those evil unwholesome states. But if, by reviewing, he knows thus: 'On the path by which I went to the village for alms, and in the place where I wandered for alms, and on the path by which I returned from the alms round, there was no desire, lust, hate, delusion, or aversion in my mind regarding forms cognizable by the eye,' then he can abide happy and glad, training day and night in wholesome states. "
​"Again, Sariputta, a bhikkhu should consider thus: 'On the path by which I went to the village for alms, or in the place where I wandered for alms, or on the path by which I returned from the almsround, was there any desire, lust, hate, delusion, or aversion in my mind regarding sounds cognizable by the ear?...regarding odours cognizable by the nose?...regarding flavours cognizable by the tongue?...regarding tangibles cognizable by the body?...regarding mind-objects cognizable by the mind?' If, by reviewing, he knows thus: 'On the path by which I went to the village for alms...there was desire, lust, hate, delusion, or aversion in my mind regarding mind-objects cognizable by the mind,' then he should make an effort to abandon those evil unwholesome states. But if, by reviewing, he knows thus: 'On the path by which I went to the village for alms...there was no desire, lust, hate, delusion, or aversion in my mind regarding mind-objects cognizable by the mind,' then he can abide happy and glad, training day and night in wholesome states."

"Again, Sariputta, a bhikkhu should consider thus: 'Are the five cords of sensual pleasure abandoned in me?' If, by reviewing, he knows thus: 'The five cords of sensual pleasure are not abandoned in me,' then he should make an effort to abandon those five cords of sensual pleasure. But if, by reviewing, he knows thus: 'The five cords of sensual pleasure are abandoned in me,' then he can abide happy and glad, training day and night in wholesome states."

"Again, Sariputta, a bhikkhu should consider thus: 'Are the five hindrances abandoned in me?' If, by reviewing, he knows thus: 'The five hindrances are not abandoned in me,' then he should make an effort to abandon those five hindrances. But if, by reviewing, he knows thus: 'The five hindrances are abandoned in me,' then he can abide happy and glad, training day and night in wholesome states. Again, Sariputta, a bhikkhu should consider thus: 'Are the five aggregates affected by clinging fully understood by me?' If, by reviewing, he knows thus: 'The five aggregates affected by clinging are not fully understood by me,' then he should make an effort to fully understand those five aggregates affected by clinging. But if, by reviewing, he knows thus: 'The five aggregates affected by clinging are fully understood by me,' then he can abide happy and glad, training day and night in wholesome states."
"Again, Sariputta, a bhikkhu should consider thus: 'Are the four foundations of mindfulness developed in me?' If, by reviewing, he knows thus: 'The four foundations of mindfulness are not developed in me,' then he should make an effort to develop those four foundations of mindfulness. But if, by reviewing, he knows thus: 'The four foundations of mindfulness are developed in me,' then he can abide happy and glad, training day and night in wholesome states. Again, Sariputta, a bhikkhu should consider thus: 'Are the four right kinds of striving developed in me?...Are the four bases for spiritual power developed in me?...Are the five faculties developed in me?...Are the five powers developed in me?...Are the seven enlightenment factors developed in me?...Is the Noble Eightfold Path developed in me? ...Are serenity and insight developed in me?' If, by reviewing, he knows thus: 'Serenity and insight are not developed in me,' then he should make an effort to develop them. But if, by reviewing, he knows thus: 'Serenity and insight are developed in me,' then he can abide happy and glad, training day and night in wholesome states. "

"Again, Sariputta, a bhikkhu should consider thus: 'Are true knowledge and deliverance realised by me?' If, by reviewing, he knows thus: 'True knowledge and deliverance are not realised by me,' then he should make an effort to realise true knowledge and deliverance. But if, by reviewing, he knows thus: 'True knowledge and deliverance are realised by me,' then he can abide happy and glad, training day and night in wholesome states."

"Sariputta, whatever recluses and brahmins in the past have purified their alms food have all done so by repeatedly reviewing thus. Whatever recluses and brahmins in the future will purify their alms food will all do so by repeatedly reviewing thus. Whatever recluses and brahmins in the present are purifying their alms food are all doing so by repeatedly reviewing thus. Therefore, Sariputta, you should train thus: 'We will purify our alms food by repeatedly reviewing thus." 

That is what the Blessed One said. The venerable Sariputta was satisfied and delighted in the Blessed One's words. 
In summary, the Buddha teaches Sariputta how a bhikkhu should review himself to make himself worthy of alms food. After alms round, the bhikkhu should review if there is any desire, lust, hate, delusion, or aversion in his mind regarding forms cognizable by the eye/ear/nose/tongue /body and mind? If present, they should abandon them ; if absent then he can abide happy and glad, training day and night in wholesome states.

A bhikkhu should also consider if the five hindrances have been abandoned in him; if not he should. He should also consider if four foundations of the mind, four kinds of striving, four bases of spiritual power, five faculties, five powers, serenity and insight, noble eightfold path, true knowledge and deliverance has been developed in him. If absent he should make effort to develop them; if present then he can abide happy and glad, training day and night in wholesome states.
References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The middle length discourses of the Buddha (Bhikkhu Bodhi)