I (i.e. Aḥmad b. al-Ḥārith al-Qazwīnī) was with my father at Sāmarrā’. My father was employed as a veterinary surgeon in the stable of Abū Muḥammad (al-Hasan al-‘Askarī) peace be on him.
Al-Musta‘īn had a mule whose like in beauty and stoutness has never been seen. Yet it refused (to have anyone on) its back and (to have) reins. The trainers had tried to make it comply but they did not have any trick by which they could ride it. One of his bosom companions said to
(al-Musta‘īn): “Commander of the faithful, send for al-Ḥasan the descendant of al-Riḍā to come, either he will ride it or it will kill him.”
He sent for Abū Muḥammad (al-Ḥasan al-‘Askarī), peace be on him. My father went with him. When Abū Muḥammad (al-Ḥasan al-‘Askarī) entered the palace, I was with my father. Abu Muḥammad (al-Ḥasan al-‘Askarī), peace be on him, looked at the mule standing in the courtyard of the palace. He went straight up to it and put his hand on its buttocks. I looked at the mule and it was sweating so that the sweat was pouring off it. Then he went to al-Musta‘īn and greeted him. The latter welcomed him, brought him close to his seat and said: “Abū Muḥammad (al-Ḥasan al-‘Askarī), put reins on this mule.”
“Put reins on it, servant,” Abū Muḥammad (al-Ḥasan al-‘Askarī) told my father.
“You, rein it,” al-Musta‘īn said to him.
Abū Muḥammad (al-Ḥasan al-‘Askarī) put on his cloak. Then he rose and put the reins on it. He went back to his place and sat down
“Abū Muḥammad ,” said al-Musta‘īn, “saddle it.”
“Servant, saddle it,” he said to my father.
“You, saddle it,” al-Musta‘īn said to him.
He rose a second time and saddled it. Then he returned.
“Do you think that you could ride it?” (al- Musta‘īn) asked him.
“Yes,” answered Abū Muḥammad (al-Ḥasan al-‘Askarī).
Then he mounted it without it resisting him. He galloped it through (the courtyard of) the palace. He made it canter at a gentle pace and then it walked beautifully. Then he came back and dismounted.
“How did you find it, Abū Muḥammad ?” al-Musta‘īn asked him.
“I have not seen its like in beauty and liveliness,” he answered.
“The Commander of the faithful gives it to you,” al-Musta‘īn told him.
“Servant, take it,” Abū Muḥammad (al-Ḥasan al-‘Askarī) ordered my father. My father took it and lead it
(Kitab Al Irshad, Chapter on Imam Hasan Askari (a.s.), Al-Kāfī, I, 507, tradition no. 4)