What is the special invocation of the Prophet Muhammad (saw) that he reserved for his followers on the Day of Resurrection?
      Narrated Anas:                          that the Prophet said, "For every prophet there is an invocation that      surely will be responded by Allah," (or said), "For every prophet      there was an invocation with which he appealed to Allah, and his      invocation was accepted (in his lifetime), but I kept my (this      special) invocation to intercede for my followers on the Day of      Resurrection."