From The Bahiya Sutta

During alms rounds, Bahiya approached the Buddha to ask a question.

“Teach me the dhamma, O Blessed One! Teach me the dhamma, O Holy One, so that it will be for my long-term welfare and bliss!”

The Buddha said to him, “This is not the time, Bahiya. We have entered the town for alms.”

Bahiya pleaded with the Buddha a second time, “Please teach me the dhamma, O Blessed One, so that I may be happy and free.”

And again, the Buddha tried to put Bahiya off saying that this was not the right time as they were on alms round.

Bahiya pleaded his case the third time.

This time the Buddha relented and said, “Bahiya, you should train yourself like this: whenever you see a form, simply see; whenever you hear a sound, simply hear; whenever you smell an aroma, simply smell; whenever you taste a flavor, simply taste; whenever you feel a sensation, simply feel; whenever a thought arises, let it be just a thought. Then ‘you’ will not exist; whenever you do not exist, you will not be found in this world, another world, or in between. That is the end of suffering.