it is never mentioned in the books .
It certainly is in the Deathly Hallows. Harry saw Snape's memories in the pensieve including the one where Dumbledore told Snape that Harry had a part of Voldemort's soul attached to his own and would finally have to face Voldemort and die. Harry accepted this and bravely walked back to the forest to Voldemort believing he would die. Dumbledore knew that Voldemort had used Harry's blood with Lily's protective enchantment to rebuild his body. He guessed that if Harry willing sacrificed himself for others, that he would cast the same protective enchantment that his mother had done for him. Further, he believed Lily's blood protection in Voldemort would tether Harry to life. He was right. That's why Harry survived.