Genesis 21:9

מצחק MAKING SPORT — This means worshipping idols, as it is said in reference of the Golden Calf, (Exodus 32:6) “And they rose up to make merry (לצחק).” Another explanation is that it refers to immoral conduct, just as you say in reference to Potiphar’s wife, (Genesis 39:17) “To mock (לצחק) at me.” Another explanation is that it refers to murder, as (2 Samuel 2:14) “Let the young men, I pray thee, arise and make sport (וישחקו) before us” (where they fought with and killed one another) From Sarah’s reply — “for the son of this bondwoman shall not be heir with my son״ — you may infer that he (Ishmael) was quarrelling with Isaac about the inheritance, saying, “I am the first-born and will, therefore, take a double portion”. They went into the field and he (Ishmael) took his bow and shot arrows at him (Isaac), just as you say (Proverbs 26:18-19) “As a madman who casteth firebrands, [arrows and death] and says: I am only מצחק mocking” (Genesis Rabbah 53:11).

וַתֵּ֨רֶא שָׂרָ֜ה אֶֽת־בֶּן־הָגָ֧ר הַמִּצְרִ֛ית אֲשֶׁר־יָלְדָ֥ה לְאַבְרָהָ֖ם מְצַחֵֽק׃

And Sara saw the son of Hagar the Miżrian, whom she had born to Avraham, mocking.