Exodus 23:19
18 “You must not offer the blood of my sacrifice with bread containing yeast; the fat of my festal sacrifice must not remain until morning. 19 The first of the firstfruits of your soil you must bring to the house of the Lord your God. “You must not cook a young goat in its mother’s milk. 20 “I am going to send a messenger before you to protect you as you journey and to bring you into the place that I have prepared.
Onkelos Exodus 23:19
18 Do not offer with unleavened bread the blood of My pascha, neither shall the fat of the sacrifice of the feast remain without on the altar until morning. 19 The beginning of the first fruits of your land you will bring into the sanctuary of the Lord God. Do not eat meat with milk. 20 Behold, I send My Angel before you, to protect you in the way, and to bring you into the place which I have prepared.
Notes and References
"... Our targumist considers the biblical command, 'you should not cook a kid in its mother's milk,' as a prohibition against eating meat and milk together. He translates the identical biblical mandate, in 34:26 and Deuteronomy 14:21, in a similar fashion. The Mekhilta and Babylonian Talmud (Chullin 15b) differ. They interpret each repetition differently - one proscribing eating, another cooking, and the third deriving benefit from the mingling of the two products. Saadiah translates the phrase here and in Deuteronomy 14:21 as 'do not cook meat and milk,' and in 34:26 as 'do not eat meat and milk.' Maimonides (in his Guide of the Perplexed 3:48) understands the verses literally. He explains that the prohibition was to wean the Israelites from a gross and degrading idol worship ceremony. Rashbam informs us that the law is placed in this biblical section because many animals were consumed during the pilgrimage festivals and it is, therefore, the appropriate place to emphasize the prohibition ..."
Drazin, Israel, and Stanley M. Wagner Onkelos on the Torah, Exodus: Understanding the Bible Text (p. 155) Gefen, 2006