R’ Yehudah says: We do not raise one to the Kehunah by the testimony of one witness. Said R’ Elazar: When? When there are contesters; but when there are no contesters, we raise one to the Kehunah by the testimony of one witness. Rabban Shimon ben Gamliel says in the name of R’ Shimon ben HaSegan: We raise one to the Kehunah by the testimony of one witness.