Genesis 15:4

And behold, the word of the Lord [came] unto him
Either having disappeared, and then came a second time, or he again spoke unto him:

saying, this shall not be thine heir;
this Eliezer, this servant of thine, as thou hast made him, or hast intended to make him, giving up all hopes of having issue by Sarai:

but he that shall come forth out of thine own bowels shall be thine
heir;
that is, one shall inherit all thou hast, that shall be begotten by thee; an own son of Abram's, and not a servant born in his house; one that should spring out of his own loins: the Vulgate Latin version renders it, "out of thy womb", that is, out of his wife's, which was his; the phrase designs a genuine and legitimate son of his, who would be legally his heir.