A monk named Yasa, travelling in the Vajji country, saw the community at Vesali collecting money from lay donors at the fortnightly recitation and objected to it. The monks of Vesali expelled him. He went out and gathered senior monks from the west and from Avanti, and what began as one man's complaint about a collection became the second council of the Buddhist order.
The Vinaya sets out ten practices at issue and most of them are small. Carrying salt in a horn against future need. Eating after the shadow has passed the mark by two finger widths. Drinking palm juice that has begun to ferment. Sitting on an unbordered mat. Taking a second meal in another village. The tenth is the one that carried weight: accepting gold and silver.
The assembly did not settle the matter by counting heads. A committee of eight was appointed, four from the east and four from the west, and it took the ten points one at a time, tracing each back to the rule it was said to break and to the occasion on which the Buddha was said to have laid that rule down. Every one was declared unlawful. The tradition then has the whole assembly recite the teaching again, and the council takes its formal name from that recitation rather than from the judgment.
What makes the account credible to historians is how unglamorous it is. No gods attend, nothing miraculous happens, and the dispute is a procedural quarrel about monastic property of a kind any religious order generates within a generation of its founder's death. A tradition inventing a founding council for itself would not have invented an argument about salt.