Mahāvacchagotta Sutta

The Paribbājaka Vacchagotta visits the Buddha at Veluvana and asks him to expound right and wrong. The Buddha does so, and adds that those who follow his teaching are sure of deliverance and of birth in happy worlds and are destined for Nibbāna. Vacchagotta is very pleased and seeks admission to the Order, but the Buddha says that he must first pass four months as a probationer. At the end of that time he enters the Order and the Buddha further expounds the Doctrine to him. Shortly after he becomes an Arahant. M.i.489 97.