The Rod Testifies the Imamat of Imam Reza (as)

Al-Husayn Bin 'Umar
He said: [I did my best with Yahyā b. Akthem (the judge of Sāmrrā'); I debated with him, conversed with him, communicated with him, and asked him about the knowledge of Mohammed's Household; yet I heard say:] "One day while I was circling the grave of Allah's Messenger, may Allah bless him and his family, I saw Mohammed b. 'Ali al-Ridā, peace be on him, circling it, so I debated with him on some questions which I had, and he answered them. The I said to him: 'By Allah, I want to ask you a question but I am ashamed of that, so he said to me: 'I will answer you before you question me, you want to ask me about the Imām.' So I replied: 'By Allah, this is what I want,' and he said: 'I am he.' Then I asked him: 'Is there any sign?' There was a rod in his hand, and the rod uttered and said: 'Surely my master is the Imām of this time, and he is the argument.' ( Usūl al-Kāfi, vol. 1, p. 353.)

Reference :The life of Imām'Ali Bin Mūsā al-Ridā