Genesis 22

Abraham's life  -- and in particular his life with God -- had its ups and downs.  He had his moments of failure, usually brought on by cowardice and unwillingness to trust God, and usually having to do with his wife Sarah.  He also had his mountaintop experiences, in which he grew as close to God as any mortal man ever did.

Genesis 22 details probably the darkest and most heartbreaking mountaintop experience in history, with the possible exception of Christ's crucifixion.