Sahih Muslim Book 32, Hadith Number 6190.

Chapter : The preference of benevolent treatment to parents over voluntary prayers, etc.

Abu Huraira reported Allah’s Messenger (may peace be upon him) as saying: Let him be humbled, let him be humbled. It was said: Allah’s Messenger, who is he? He said. He who finds his parents in old age, either one or both of them, and does not enter Paradise.