Miszna do Psalmów 78:34

And why do they record the opinion of a single person among the many, when the halakhah must be according to the opinion of the many? So that if a court prefers the opinion of the single person it may depend on him. For no court may set aside the decision of another court unless it is greater than it in wisdom and in number. If it was greater than it in wisdom but not in number, in number but not in wisdom, it may not set aside its decision, unless it is greater than it in wisdom and in number.