… when people put clean things, unclean things, excrement, urine, saliva, pus, or blood on the earth, the earth is not bothered, humiliated, or disgusted, in the same way, Rāhula, practice ‘peacefulness of earth’ meditation.

Then Venerable Rāhula, thinking “How could one who has been personally advised by the Blessed One enter a village for alms?” turned back, sat at the base of a tree, crossed his legs, set his body upright, and established mindfulness.

The Buddha tells Rāhula to meditate on not-self, which he immediately puts into practice. Seeing him, Venerable Sāriputta advises him to develop breath meditation, but the Buddha suggests a wide range of different practices first.