Musannaf Ibn Abi Shaybah 8340 — Over what distance the prayer

Yahya bin Yazid al-Huna'i said: I asked Sayyiduna Anas bin Malik (may Allah be pleased with him) about shortening the prayer, and he said: When the Messenger of Allah (peace and blessings be upon him) set out on a journey of three miles or three farsakhs, he would shorten the prayer. (Shu'bah is the one who was in doubt.)