Mutawakkil ordered to arrest Imam al-Hadi (a.s.) and put him in prison. After some days in prison, Saqr bin Abu Dulaf came to visit him. The chamberlain, who knew him and knew that he was a Shia, received and asked him, ‘What do you want and what for you have come?’
He said, ‘I have come for good.’
The chamberlain said, ‘You might have come to ask about your master!’
He said, ‘My master is Ameerul Mo’minin (he meant al-Mutawakkil).’
The chamberlain smiled and said, ‘Be silent! Your master is the truth (he meant Imam al-Hadi). Do not fear me! I am on your belief.’
Saqr said, ‘Praise be to Allah!’
The chamberlain said, ‘Do you want to see him?’
Saqr said, ‘Yes, I do.’
The chamberlain said, ‘Sit down here until the mailman comes out.’
When the mailman went out, the chamberlain said to his attendant, ‘Take Saqr to the room where the Alawid is imprisoned and leave them alone!’ When Saqr went into the cell, he saw Imam al-Hadi (a.s.) sit on a mat and before him there was a dug grave. Al-Mutawakkil had ordered this grave to be dug in order to frighten the imam. Imam al-Hadi (a.s.) said to Saqr kindly and friendly, ‘O Saqr, what made you come?’
Saqr said, ‘I came to know your news.’ Saqr began crying feeling pity and fear for the imam. The imam said to him, ‘O Saqr, do not worry. They cannot harm us.’
Saqr calmed down and thanked Allah for that. Then he asked the imam about some religious questions and the imam answered his questions. Then he said farewell to the imam and left. It was no long after that when the imam was set free. ( Bihar al-Anwar.)