Volume 8, Book 77, Number 615:
Narrated Ibn ‘Umar:
The Prophet said to Ibn Saiyad, “I have kept for you a secret.” Ibn Saiyad said, “Ad-Dukh.” The
Prophet said, “Keep quiet, for you cannot go beyond your limits (or you cannot exceed what has been
foreordained for you).” On that, ‘Umar said (to the Prophet ), “Allow me to chop off his neck!” The
Prophet said, “Leave him, for if he is he (i.e., Ad-Dajjal), then you will not be able to overcome him,
and if he is not, then you gain no good by killing him.”