Musnad Abu Ya'la al-Mawsili 209:151

Abu Khaythama narrated to us, Muhammad ibn Yazid al-Wasiti narrated to us, from al-Qasim ibn al-Fadl, from Abu Ja'far Muhammad ibn Ali, from Umm Salamah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Hajj is the Jihad of every weak person."