Mishnah 16 - Chapter 1 - Pirkei Avot

R. Gamliel was wont to say [in respect to hora'ah (halachic rulings): If a question comes before you and you are in doubt (as to the halachah),] make a rav for yourself, and remove doubt from yourself [(and do not rule alone) as in the instance of Rava (viz. Horiyoth 3b). When a question of treifah (ritually unfit meat) came before him, he would gather together all the butchers of Mata Mechasia, saying "so that each take a chip of the beam" (i.e., so that the entire onus not fall on him alone)]. And do not tithe overmuch by estimate. [For one who does so is not spared defect. If he tithes too little, his tithes are correct, but his fruits are "defective"; and if he tithes too much, his fruits are "corrected," but his tithes are defective.]