Genesis 23:2

וַתָּמָת שָׂרָה בְּקִרְיַת אַרְבַּע הִוא חֶבְרוֹן בְּאֶרֶץ כְּנָעַן וַיָּבֹא אַבְרָהָם לִסְפֹּד לְשָׂרָה וְלִבְכֹּתָהּ

Sarah died in Kiryat Arba, which is Chevron, in the land of Canaan, and Avraham came to mourn for Sarah and to cry for her.

The letter kaf in the word “v’livkosa” (to cry for her) is written smaller than the other letters. If that letter is ignored, the word would be read “u’lbita” – that Avraham went to mourn for Sarah “and for her daughter,” suggesting that Avraham and Sarah had a daughter, who also died. The Talmud in Baba Basra (16b) discusses Genesis 24:1, that G-d blessed Avraham “with everything” (“bakol”). Rabbi Yehuda’s opinion there is that this means that Avraham must also have had a daughter. Some say that this girl’s name actually was “Bakol” (“with everything”).