Musnad Ahmad 30:3577

Ad-Dahhak narrated to us, Hajjaj as-Sawwaf narrated to us, Yahya ibn Abi Kathir narrated to us, from Abu Ja'far, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Three supplications are answered, there is no doubt in them: the supplication of the parent against their child, the supplication of the oppressed, and the supplication of the traveler."