Musannaf Ibn Abi Shayba 33:709

Muhammad ibn Fudayl narrated to us, from Ibrahim, the mu'adhdhin of Banu Hanifa, who said: I saw Mahan al-Hanafi, and al-Hajjaj had ordered that he be crucified at his door. He said: So I looked at him while he was upon the wooden beam, and he was glorifying Allah (saying SubhanAllah), magnifying Him (saying Allahu Akbar), declaring His oneness (saying La ilaha illa Allah), and praising Him (saying Alhamdulillah) until he reached twenty-nine, and he knotted [his fingers] to twenty-nine with his hand. Then he was stabbed while he was in that state. I saw him after a month, and his hand was still knotted at twenty-nine. He said: And light used to be seen with him at night.