Anupubbikathā

Vinayapiṭaka · Cūḷavagga (2) · Vol. 7 · Section 390

[390] Now at that time about five hundred bhikkhus, Vajjiputtakas of Vesālī, were newly ordained and inexperienced (appakataññuno). And they, thinking, "This is the Dhamma, this is the Vinaya, this is the Teacher's instruction," took the voting tickets (salākā). Then Devadatta, having split the Saṅgha, taking with him about five hundred bhikkhus, departed for Gayāsīsa.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.