And he said, Take now thy son, thine only son Isaac, whom thou lovest, and ... offer him there for a burnt offering.... And Abraham stretched forth his hand, and took the knife to slay his son. Genesis 22:2,10God told the Israelites to sacrfice their firstborn sons to him.
Because thou hast done this thing, and hast not withheld thy son, thine only son ... I will bless thee. Genesis 22:16-17
Sanctify unto me all the firstborn, whatsoever openeth the womb among the children of Israel, both of man and of beast: it is mine. Ex.13:2And Jephthah sacrificed his daughter to God. (God apparently approved of Jephthah's sacrfice since he is listed as a hero of faith in Hebrews 11:32.)
Thou shalt set apart unto the LORD all that openeth the matrix, and every firstling that cometh of a beast which thou hast; the males shall be the LORD's. And every firstling of an ass thou shalt redeem with a lamb; and if thou wilt not redeem it, then thou shalt break his neck: and all the firstborn of man among thy children shalt thou redeem. Ex.13:12
Then the Spirit of the LORD came upon Jephthah ... And Jephthah vowed a vow unto the LORD, and said, If thou shalt without fail deliver the children of Ammon into mine hands, Then it shall be, that whatsoever cometh forth of the doors of my house to meet me, when I return in peace from the children of Ammon, shall surely be the LORD's, and I will offer it up for a burnt offering. ... And the LORD delivered them into his hands. And he smote them ... with a very great slaughter. ... And Jephthah came to Mizpeh unto his house, and, behold, his daughter came out to meet him with timbrels and with dances. ... I have opened my mouth unto the LORD, and I cannot go back. ... And ... her father ... did with her according to his vow which he had vowed. Judges 11:29-39