Midrash su Deuteronomio 15:23

8) Since bechor is outside the category of consecrated animals which have been rendered pasul, (in that it is eaten in its blemished state and is not redeemed), I might think that eating its blood comes under two interdicts (that of eating blood and that of a non-Cohein eating consecrated food). It is, therefore, written (of such an instance, Devarim 15:23): "Only its blood you shall not eat." It falls only under one exhortation (that against eating blood, but not that against a non-Cohein eating consecrated food). This tells me only of its blood. Whence do I derive (the same for) its fat? From: "all fat and all blood." Just as the blood comes under one interdict, so, the fat.