Why Imam Reza(AS) is Called The Guarantor of The Deer?

Sheikh Saduq narrates this event in a different way in his book Uyoon Akhbar al-Ridha, where he mentions that after the martyrdom of Imam Reza (AS), a deer, fleeing from a hunter, sought refuge near the wall of Imam Reza’s shrine. The Sheikh writes that:

Abu Mansoor bin Abdul Razzaq... said... when I was young, I had a bad opinion of the visitors to Mashhad (the shrine of Imam Reza) and would rob their belongings—clothes, money, letters, and other possessions. One day, I went hunting and released a cheetah after a deer. The cheetah chased the deer until the deer, frightened, took refuge by a wall and stopped. The cheetah stopped as well but did not approach the deer. I tried to push the cheetah closer to the deer, but it remained still. However, whenever the deer moved away from the wall, the cheetah would follow. But as soon as the deer retreated to the wall, the cheetah backed off. Eventually, the deer entered a hole in the wall, and I entered the nearby shelter and asked, "Where is the deer that just entered the shelter?" They replied, "We did not see any deer."

I went back to the hole where the deer had entered and saw its footprints, but I could not find the deer itself. Then, I made a vow to God that I would no longer harm the pilgrims and would treat them kindly.

In Bihar al-Anwar, another account of a similar story is recorded during the reign of Sultan Sanjar. The prince, who was ill, had gone hunting, and a deer fled to the shrine. Upon seeing this, the prince threw himself at the tomb and was healed. In gratitude, Sultan Sanjar built a dome over the grave.

The most famous story related to the title "The Guarantor of the Deer" is as follows: A hunter in the desert chases a deer, which runs a considerable distance. Eventually, the deer takes refuge with Imam Reza (AS), who happens to be nearby. When the hunter tries to capture the deer, Imam Reza (AS) stops him. The hunter insists on capturing the deer, claiming it is his right. Imam Reza (AS) offers to pay more than the value of the deer to the hunter, but the hunter refuses. At that point, the deer speaks and explains that it has two hungry fawns waiting for its milk. The deer asks Imam Reza (AS) to guarantee its return after it feeds its young. Imam Reza (AS) agrees to be the guarantor. The deer leaves and returns after feeding its fawns, willingly submitting to the hunter. Seeing this loyalty, the hunter is moved and soon realizes that the guarantor is none other than Imam Reza (AS). He releases the deer and apologizes to Imam Reza (AS), who blesses him and promises to intercede for him on the Day of Judgment. The deer, now freed, leaves to reunite with its fawns.