Leviticus 22:28

The cow or ewe, and her young, in one day This Maimonides considers as a precaution of humanity, lest the dam should be brought to the altar while she is yet mourning the loss of her young, slain perhaps before her eyes. And, indeed, there is a degree of cruelty in the very idea of imbruing the hand in the blood of both parent and offspring at the same time. Therefore Jonathan, in his paraphrase, considers this as a symbolical precept, to teach the Israelites to be merciful, as their Father in heaven is merciful.