This is as I heard. At one time, the Buddha was living in the city of Rājagaha, in the Bamboo Garden, in the squirrels’ feeding ground.
Bilaṅgika of the brahmin caste heard a rumour that a man from his clan had become a monk under the Buddha. Bilaṅgika was not happy about this. He got angry, went to the Buddha and was standing silently and angrily.
Then the Buddha read Bilaṅgika’s mind and told him in verse:
“Whoever hates a pure person who does not hate anyone,
the evil backfires back on the fool,
like fine dust thrown against the wind.”
When the Buddha taught this Dhamma, Bilaṅgika said to the Buddha, “Excellent, Master Gotama! Excellent! Just as if someone turned upright, what was upside down, revealed what was hidden, pointed out the path to whoever was lost, or lit a lamp in the dark so people with good eyes could see what’s there, Master Gotama taught me the Dhamma, which is clear in many ways. I go for refuge to Master Gotama, to the Dhamma, and to the Saṅgha. Bhante, may I become a monk under you?”
And he became a monk under the Buddha. Not long after his ordination, Bhante Bilaṅgika, living alone, withdrawn, diligent, passionate, and firm, soon realized the supreme goal of the spiritual path in this very life. He achieved with his own wisdom the goal for which a son would leave the lay life to become a monk.
He realized: “Rebirth has ended. The spiritual journey has been completed. What had to be done to end suffering has been done. There will be no rebirth.” Therefore, Bhante Bilaṅgika became one of the enlightened monks.