Mishkat al-Masabih #3712

He reported God's Messenger as saying, “If one enters a horse with two others there is no good in it if he is certain it cannot be beaten, but there is no harm if he is not." It is transmitted in Sharh as-sunna. In Abu Dawud’s version he said, “If one enters a horse with two others when he is not certain that it cannot be beaten, it is not gambling; but when one enters a horse with two others when he is certain it cannot be beaten, it is gambling."