Sunan Ibn Majah, Chapter: The Chapters on Tribulations

"When Ali bin Abu Talib came to Basrah, he entered upon my father and said: 'O Abu Muslim, will you not help me against these people?' He said: 'Of course.' So he called a slave woman of his and said: 'O slave woman, bring me my sword.' So she brought it, and he unsheathed it a span, and (I saw that) it was made of wood. He said: 'My close friend and your cousin (saw) advised me, if tribulation (Fitnah) arose among the Muslims, that I should take a sword of wood. If you wish I will go out with you.' He said: 'I have no need of you or of your sword.'"