וַתֵּ֨רֶא שָׂרָ֜ה אֶֽת־בֶּן־הָגָ֧ר הַמִּצְרִ֛ית אֲשֶׁר־יָלְדָ֥ה לְאַבְרָהָ֖ם מְצַחֵֽק׃
And Sarah saw the son of Hagar the Egyptian, whom she had borne unto Abraham, making sport.
Read kabbalistic (mystical) interpretation of Genesis 21:9: and classical mystical sources.