At the end of one rains retreat (vassa), the Buddha was so pleased with the progress of the assembled monks that he encouraged them to extend their retreat for yet another month. On the full-moon day marking the end of that fourth month of retreat, he presented his now-famous instructions on mindfulness of breathing (anapanasati), which may be found in the Anapanasati Sutta (MN 118) - The Discourse on Mindfulness of Breathing.
