Musannaf Ibn Abi Shayba 3:5793

Hatim ibn Isma'il narrated to us, from 'Abd al-Rahman ibn Harmala, that he heard a man asking Sa'id ibn al-Musayyib: "Should I complete the prayer and fast while traveling?" He said: "No." He said: "But I am strong enough for that." He said: "The Messenger of Allah (may Allah bless him and grant him peace) was stronger than you, and he used to shorten the prayer during travel and break his fast." And the Messenger of Allah (may Allah bless him and grant him peace) said: "The best of you is the one who shortens the prayer during travel and breaks his fast."