Genesis 18:1 And the LORD appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day;

Genesis 17:1 And when Abram was ninety years old and nine, the LORD appeared to Abram, and said unto him, I am the Almighty God;

After God affirms the covenant with Abram, the Bible now moves on to tell us more about Sarai, his wife. Sarai had not, at this point, had any children with Abram. This is a source of stress for Sarai.

Genesis 16:2 And Sarai said unto Abram, Behold now, the LORD hath restrained me from bearing: I pray thee, go in unto my maid; it may be that I may obtain children by her. And Abram hearkened to the voice of Sarai.