I think I found it:
"The Prophet (sal-Allaahu 'alayhe wa sallam) said,'Three men will be
killed at the place where your treasure is. Each of them will be the son of
a Khaleefah, and none of them will get hold of the treasure. Then the
black banners will come out of the East, and they will slaughter you in a
way which has never been seen before.' Then he said something which I
do not remember; then, 'If you see him, go and give him your allegiance,
even if you have to crawl over ice, because he is the Khaleefah of Allaah,
the Mahdee.'" [Ibn Maajah] 
The treasure referred to in this text is the treasure of the Ka'bah. Towards
the end of time, three of the sons of the Khaleefahs will fight to get hold
of it, until the Mahdee appears. He will appear from the East, not from the
tunnel of Saamarraa, as the Shee'ah claim; they believe that he is in this
tunnel now, and they are waiting for him to emerge at the end of time.
There is no evidence for it in any book or Saheeh tradition, and there is
no benefit in believing this.
The truth of the matter is that the Mahdee whose coming is promised at
the end of time will appear from the East,and people will swear allegiance
to him at the Ka'bah, as some Ahaadeeth indicate.
Allah a3lam maybe they'll be fighting for power.. I have been thinking about this alot of late..
but everything is unraveling as if in a string of pearls.. it is just so amazing to watch...