Dhul-Kifl was a Prophet sent to Bani Israel (Israelites). He was known as Ezekiel by Jews who greatly revered him.

He was described by Allah in the Quran as a patient and righteous servant of Allah

He is said to be the successor of Prophet Al-Yasa (Elisha).

Iblis (Shaitan) came to know of his righteousness, patience and the fact that he never got angry, so he took it as a personal challenge to make Dhul-Kifl loose his patience and become angry.

Dhul-Kifl used to fast during the day and make prayer remembering Allah throughout the night. In the afternoon he would take a nap to rejuvenate himself.

Iblis decided to disturb Dhul-Kifl during his afternoon nap. Disguised as an old man Iblis came to the door of Dhul-Kifl and knocked. When the door was opened he said “I am an old man and I have been wronged. There is enimity between me and my people and they are doing injustice to me, so please help me.” He stretched his story so long that the napping time for Dhul-kifl was over, he asked the  old man to visit his court the next day so justice could be done.

Next day Dhul-Kifl waited for the old man (Iblis) who did not show up. He returned home and had just begun his nap when the old man came to his house again banging the door .

When questioned why he did not come to court in the morning, the old man replied “ My people are very clever, once they knew you would be sitting in the court, they agreed to settle the matter out of the court. But as soon as you left the court they went back on their promise” He continued the conversation till the nap time was finished and a second day passed without sleep for Dhul-Kifl.

Once again he asked the old man to come to court the next day. But the next day also the old man (Iblis) failed to show up in the court. A tired Dhul-Kifl because of lack of sleep asked his family members not to allow anyone to knock at his door as he really needed the sleep.

Iblis was happy with his success and was sure that this time Dhul-Kifl would not only become impatient and angry but would not be able to fast and pray. He once again visited his house. Dhul-Kifl family members stopped him this time but Iblis was determined to get in.

He did so by climbing up the wall and into the room. When Dhul-Kifl saw the old man in his room he was shocked to see him inside while the door remained shut. Then he suddenly became aware that the man standing in front of him was not human.

So he asked him “Are you the enemy of Allah?”  Iblis in disguise of the old man said “Yes, and you have foiled all my attempts to make you angry and impatient.”

It was said that it was because of this episode that Allah called him Dhul-Kifl because he took responsiblity of doing something and always completed it. He was neither impatient or angry even though tired.

Reference :

Stories of the Prophets (Ibn Kathir); Wikipedia.