Miracles

The student who undergoes intense training in a spiritual retreat will sometimes gain the power of working some extraordinary feats as he progresses. It was usually tempting for them to display these abilities to the masses instead of continuing the hard path of spiritual training. Only the most serious pupils avoided this miracle mongering which delighted the crowds.

Imam al-Junayd got angry with his student (Nuri) for performing a miracle in public. The miracle involved him walking on the Tigris river to catch a certain fish (which he succeeded in catching). His reputation was greatly enhanced by this extraordinary event. Junayd said that he would have preferred a viper come out of the river and punish his ignorant student.

Notes

Karamat: Miracle of Saints (Awliya)
Mu'jizat: Miracle of Prophets (Anbiya)

Karamat involves secrecy
Mu'jizat involves publicity

* Miracle stories of this kind can be found in all of the spiritual traditions. 

"A beautiful story is told of Abū-Sa'īd ibn Abul-Khair. Someone told him of a mystic who walked on water, and he replied "Frogs and waterfowl do that aswell!" When the person said, "and so-and-so flies in the air!" and he replied "So do birds and insects!" And when the narrator told him that somebody went from one town to the other in one minute, he answered: "Satan goes in one moment from the East to the West!" On another occasion he reproached somebody who asked what kind of miracles a certain Sufi had to his credit by drawing attention to the life story of the saint in question: Is it not the greatest miracle that a butcher, who was also a butchers son, should be attracted to the mystical Path, talk to Khidr, and be visited by innumerable people who want to obtain his blessing?"

 - Annemarie Schimmel 

Source: Mystical Dimensions of Islam, page 211-212