Imam Al-Nawawi’s Riyad-us-Saliheen
Desirability of Supplications during the Journey
980. Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (sallallaahu alayhi wa sallam) said, “Three supplications are answered without doubt. The supplication of the oppressed, the supplication of the traveller, and the supplication of the parent for his son.”
[At-Tirmidhi and Abu Dawud].