פירוש על עבודה זרה 82:10

A haver is someone known to tithe his food. This haver dies leaving a store room full of produce, and we do not know whether it has been tithed or not. The produce was certainly untithed at one point (this would be true of all produce). But now the “doubt” about whether it was tithed seems to be significant enough to presume that the produce is tithed. Thus a doubt sets aside a certainty.