It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "There are three supplications that are not turned back: the supplication of the father, the supplication of the fasting person, and the supplication of the traveller."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6392