Musannaf Ibn Abi Shayba 36:325

Yazid ibn Harun narrated to us, he said: al-Dastawa'i informed us, from Yahya ibn Abi Kathir, from Abu Ibrahim al-Ansari, from Abu Sa'id al-Khudri, that the Prophet, may Allah bless him and grant him peace, shaved on the day of al-Hudaybiyyah, he and his companions, except for Uthman and Abu Qatadah. The Messenger of Allah, may Allah bless him and grant him peace, said: "May Allah have mercy on those who shave." They said: "And those who shorten?" He said: "May Allah have mercy on those who shave." They said: "And those who shorten, O Messenger of Allah?" He said: "May Allah have mercy on those who shave." They said: "And those who shorten, O Messenger of Allah?" He said: "And those who shorten."