Musannaf Ibn Abi Shayba 3:2401

Ghundar narrated to us, from Shu'bah, from 'Abd al-Khaliq, from Hammad, who said: If one forgets a prayer while at home (in residence) and remembers it while traveling, he shall pray it as four [rak'ahs]. And if one forgets a prayer while traveling and remembers it while at home, he shall pray it as a travel prayer.