Berakhot

From what time may the Shema’ be read in the evening? From the time the priests enter [the Temple] to partake of their Terumah, until the end of the first watch. These are the words of R. Eliezer; but the Sages say: Until midnight.

Rabban Gamaliel says: Until the rise of dawn.

It once happened that his sons returned from a feast [after midnight] and said to him, “We have not read the Shema’!” He told them, “If the dawn has not yet risen, you are still under the obligation of reading it. And not only in this connection do they so decide; but wherever the Sages use the expression ‘Until midnight,’ the obligation continues until the rise of dawn.”

The duty of burning the fat and parts of the animal continues until the rise of dawn. Likewise with all offerings which have to be eaten the same day [they are sacrificed], the duty continues until the rise of dawn. If so, why do the Sages say “Until midnight”? In order to keep a man far from transgression.