Abu Mihjan al-Thaqafi Against the Persians
During the battle, Hazrat Salama bint Hafsa (ra), the wife of Hazrat Sa‘d (ra), saw a prisoner who was shackled in chains and expressed immense longing to participate in the battle. His name was Abu Mihjan al-Thaqafi. He also happened to arrive at the [location of the battle] after Hazrat Umar (ra) expelled him [from the city] due to him drinking alcohol. However, after being guilty of drinking alcohol again, Hazrat Sa‘d (ra) punished him with lashes and tied him in chains.
Abu Mihjan requested Zahrah, who was a maidservant of Hazrat Sa‘d (ra), to open his chains so that he could participate in the battle. He stated, “By Allah, if I survive, I will return and put on the chains again.” The maidservant accepted his request and opened the chains. Abu Mihjan mounted the horse of Hazrat Sa‘d (ra) and headed towards the battlefield. Penetrating the rows of the enemy, he headed towards the big white elephant and attacked it. Hazrat Sa‘d (ra) was observing all of this at the time and said, “Although the horse belongs to me, however, the one riding it appears to be Abu Mihjan al-Thaqafi.” As mentioned previously, Hazrat Sa‘d (ra) could not actively participate in the battle due to illness, but he was supervising from further afield. In any case, the fighting continued for three days. When the battle came to an end, Abu Mihjan al-Thaqafi returned and put on his chains again. Hazrat Sa‘d (ra) released Abu Mihjan saying, “If you drink alcohol again, I shall hand out a severe punishment.” Abu Mihjan promised never to drink again. According to another narration, Hazrat Sa‘d (ra) wrote about the entire incident to Hazrat Umar (ra), upon which Hazrat Umar (ra) said, “If he repents from drinking alcohol again, then he should not be punished.” Upon this, Abu Mihjan swore to never drink again and Hazrat Sa‘d (ra) set him free.
(Ashra Mubashra, Bashir Sajid, pp. 850-851)