Narrated Yahya b. Yazid al-Hannani:I asked Anas b. Malik about the shortening of the prayer (while travelling). He said: When the Messenger of Allah (ﷺ) went out on a journey of three miles or three farsakh (the narrator Shu'bah doubted), he used to pray two rak'ahs

English translation · Sunan Abu Dawud