3 occurrences across the corpus

Sefer haYashar (Book of Jasher)

The Book of Jasher 25:16

And Ribah bare unto Ishmael Nebayoth, Kedar, Adbeel, Mibsam and their sister Bosmath.

The Book of Jasher 29:12

And when Esau saw that Jacob had fled and escaped from him, and that Jacob had cunningly obtained the blessing, then Esau grieved exceedingly, and he was also vexed at his father and mother; and he also rose up and took his wife and went away from his father and mother to the land of Seir, and he dwelt there; and Esau saw there a woman from amongst the daughters of Heth whose name was Bosmath, the daughter of Elon the Hittite, and he took her for a wife in addition to his first wife, and Esau called her name Adah, saying the blessing had in that time passed from him.

The Book of Jasher 30:17

And in the third year of Jacob's dwelling in Haran, Bosmath, the daughter of Ishmael, the wife of Esau, bare unto him a son, and Esau called his name Reuel.