Hindu History
This was the day when Vyasa – author of the Mahabharata – was born to sage Parashara and a fisherman’s daughter Satyavati; thus, this day is also celebrated as Vyasa Purnima. Veda Vyasa did yeoman service to the cause of Vedic studies by gathering all the Vedic hymns extant during his times and dividing them into four parts based on their characteristics and use in rites. He then taught them to his four chief disciples – Paila, Vaisampayana, Jaimini and Sumantu. It was this dividing and editing that earned him the honorific “Vyasa” (vyas = to edit, to divide). He divided the Vedas into four parts, namely Rig, Yajur, Sama and Atharva.
Buddhist History
Gautama Buddha went from Bodhgaya to Sarnath about 5 weeks after his enlightenment. Before he attained enlightenment, he gave up his austere penances. His former comrades, the pañcavargika, left him and went to Ṛṣipatana in Sarnath.
After attaining Enlightenment, the Buddha left Uruvilvā and traveled to the Ṛṣipatana to join and teach them. He went to them because, using his spiritual powers, he had seen that his five former companions would be able to understand Dharma quickly. While travelling to Sarnath, Gautama Buddha had to cross the Ganges. When King Bimbisara heard of this, he abolished the toll for ascetics.
When Gautama Buddha found his five former companions, he taught them the Dharmacakrapravartana Sūtra. They understood and also became enlightened. This marked the establishment of the mendicant Sangha, on the full-moon day of Asadha. The Buddha subsequently spent his first rainy season at Sarnath at the Mulagandhakuti.
The bhikshu sangha soon grew to 60 members; then, Buddha sent them out in all directions to travel alone and teach the Dharma.