This Bible contradiction is from the EvilBible.com.
Galatians 4:22 View context
For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
Only one son
Hebrews 11:17 View context
By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten [son],