Sayyiduna Hamzah bin Amr al-Aslami (may Allah be pleased with him) narrates: He said, "O Messenger of Allah! I find in myself the strength to fast while traveling. Will there be any sin upon me (if I fast)?" The Prophet (peace and blessings be upon him) said: "It is a concession from Allah Almighty; whoever accepts it does well, and whoever wishes to fast, there is no sin upon him." The chain of this narration is authentic. Hisham bin Urwah differed in its chain; he narrated it from Sayyidah Aisha (may Allah be pleased with her), from his father, that Sayyiduna Hamzah bin Amr had asked the question. It is possible that both narrations are correct; and Allah Almighty knows best.