Reference for Chullin 61:3

וכי תימא דמכסו ליה והאמר רבי זירא אמר רב

And should you say that he covered the blood [where it fell on the ground, this is not sufficient], for R'Zera taught in the name of Rab: He who slaughters [a bird or a wild beast] must place dust underneath [the blood] and dust above it, for it is written.

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