Abraham the second son by riddle
From Sensus Plenior
Abraham the second son by riddle Just so there is no misunderstanding about the desolation of Abram, Paul, in writing to the Hebrews confirms our method of interpretation. He calls Isaac, Abraham's only-begotten son. Though Abraham had many more sons, the only one that counts as a son of Abraham is Isaac because he is the child of promise. 
- Ge 11:26 And Terah lived seventy years, and begat Abram, Nahor, and Haran.
- Ge 17:5 Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee.
- Ge 16:15 ¶ And Hagar bare Abram a son: and Abram called his son’s name, which Hagar bare, Ishmael.
- Heb 11:17 By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten [son],