Musannaf Ibn Abi Shayba 16:508

Abu Bakr narrated to us, he said: Muhammad ibn Abdullah al-Asadi narrated to us, from Ubaydullah ibn Abdullah ibn Mawhab, he said: My paternal uncle narrated to me, from Abu Hurayrah, from Uthman, he said: The Messenger of Allah, may Allah bless him and grant him peace, forbade the *mu'asfar* (garments dyed with safflower).