Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) says: I had some dates in my storeroom, and I began to notice that they were decreasing. I mentioned this to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Tomorrow you will find a cat in it; say: Answer the Messenger of Allah (peace and blessings be upon him)." When the next day came, I found a cat in it, and I said: Answer the Messenger of Allah (peace and blessings be upon him). It turned into an old woman and said: I adjure you by Allah to let me go, for I will not come back. So I let her go. Then I came to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "What did the man and his captive do?" I told him her story, and he (peace and blessings be upon him) said: "She lied; she will certainly come back. Say to her: Answer the Messenger of Allah (peace and blessings be upon him)." Then she again turned into an old woman and said: O Abu Ayyub! I adjure you by Allah to let me go this time, for I will not come back. So I let her go; then I came to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said to me the same as he had said before. I did this three times, and the third time she said to me: O Abu Ayyub! I adjure you by Allah to let me go so that I may teach you something which, when a devil hears it, he does not enter that house. I asked: What is it? She said: Ayat al-Kursi; no devil hears it but that he flees. I mentioned this to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "She spoke the truth, even though she is a liar."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3997