וְתִמְנַ֣ע ׀ הָיְתָ֣ה פִילֶ֗גֶשׁ לֶֽאֱלִיפַז֙ בֶּן־עֵשָׂ֔ו וַתֵּ֥לֶד לֶאֱלִיפַ֖ז אֶת־עֲמָלֵ֑ק אֵ֕לֶּה בְּנֵ֥י עָדָ֖ה אֵ֥שֶׁת עֵשָֽׂו׃
And Timna was a concubine to Elifaz the son of Eisav, and she bore to Elifaz Amalek. These are the sons of Adah the wife of Eisav.
Torah Temimah points to Sanhedrin 99b.
ותמנע היתה פילגש — למה נכתבה? ללמדך שחזרה אחר אברהם יצחק ויעקב להתגייר ולא קיבלוה, הלכה והיתה פילגש לאליפז בן עשו.
“And Timna was a concubine” — why was this written? To teach you that she sought after Avraham, Yitzchak and Yaakov to convert, and they did not accept her; she went and became a concubine to Elifaz the son of Eisav.
The Gemara explains the background of Timna’s status and the origin of Amalek.
Derash on the origin of Amalek (Bavli).
Timna’s rejection by the patriarchs led to her becoming the mother of Amalek through Elifaz.