Musnad Abu Ya'la al-Mawsili 3:309

Ubayd Allah narrated to us, Abdullah ibn Ja'far narrated to us, Zayd ibn Aslam informed me, from Abu Sinan Yazid ibn Umayyah al-Dayli, who said: Ali ibn Abi Talib became severely ill, to the point that he was bedridden, and we feared for him. Then he recovered and regained his strength. We said, "Congratulations to you, Abu al-Hasan. Praise be to Allah who has restored your health; we were fearing for you." He said, "But I did not fear for myself. The Truthful, the Believed informed me that I will not die until I am struck upon this"—and he pointed to the front left side of his head—"so that this will be dyed with blood from it." He took hold of his beard and said, "The most wretched of this nation will kill me, just as the most wretched of the tribe of Thamud hamstrung the she-camel of Allah." He said: The Messenger of Allah (peace and blessings of Allah be upon him) attributed him to his thigh, the lower part, not [the tribe of] Thamud.