Kathir bin Qunbur (may Allah have mercy on him) said: We asked Salim bin Abdullah (may Allah have mercy on him) about the prayer of his father (Sayyiduna Ibn Umar, may Allah be pleased with them both) while travelling, and he told me from his father that the Messenger of Allah (peace and blessings be upon him) said: "When a matter confronts one of you which he fears will be missed, let him pray this prayer", meaning combining two prayers.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13176