Musannaf Ibn Abi Shayba 3:2397

Abu Bakr narrated to us, he said: Hushaym narrated to us, he said: Yunus informed us, from al-Hasan, that he used to say regarding the traveler: If he forgets a travel prayer and remembers it while at home, he should pray the travel prayer. And if he forgets a prayer while at home and remembers it while traveling, he should pray the prayer of the home.