From Rigpa Wiki
Chökhor Düchen (Wyl. chos 'khor dus chen), the 'Festival of Turning the Wheel of Dharma' — one of the four major Buddhist holidays. It occurs on the fourth day of the sixth Tibetan lunar month. For seven weeks after his enlightenment, Buddha did not teach. Finally, encouraged by Indra and Brahma, he turned the Wheel of Dharma for the first time, at Sarnath, by teaching the ‘Four Noble Truths’.