I forget who asked and where.
This is the only place I remember it being mentioned.

HP-3, Chapter 22, Owl Post Again (last chapter) page 425

“Didn't make any difference?” said Dumbledore quietly. “It made all the difference in the world, Harry. You helped uncover the truth. You saved an innocent man from a terrible fate.”
(Recall Trelawney's prediction...)

“But – I stopped Sirius and Professor Lupin from killing Pettigrew! That makes it my fault if Voldemort comes back!”

“It does not,” said Dumbledore quietly. “Hasn't your experience with the Time-Turner taught you anything, Harry? The consequences of our actions are always so complicated, so diverse, that predicting the future is a very difficult business indeed... Professor Trelawney, bless her, is living proof of that... You did a very noble thing, in saving Petigrew's life.”

“But if he helps Voldemort back to power – !”

“Pettigrew owes his life to you. You have sent Voldemort a deputy who is in your debt... When one wizard saves another wizard's life,it creates a certain bond between them... and I'm much mistaken if Voldemort wants his servant in the debt of Harry Potter.”

“I don't want a connection with Pettigrew!” said Harry. “He betrayed my Parents!”

“This is magic at its deepest, its most impenetrable, Harry. But trust me.. the time may come when you will be vary glad you saved Pettigrew's life.”