Daraqutni

Abu Ubaid, the narrator, has reported these words in the hadith of the Prophet (peace be upon him): "There is no reality in jallab and janab." The narrator says: Jallab occurs only in two things. One is in horse racing, and its method is that a person rides behind the horse and pulls the horse, which causes the horse distress, so it has been prohibited. The second is janab in rak‘at, which is that the one who is to receive charity stays in place and then sends someone to buy various kinds of fruits from people and collects his charity; this has been prohibited. Rather, the instruction is that he should go to the people and collect charity from them by going to their homes. As for janab, what is meant by it is this: a person keeps his horse, on which he is to participate in the competition, alongside another horse on which no one is riding, and when he reaches near the finish line, he mounts the horse that was running empty, and in this way, he wins the race, because that horse will be less tired compared to the horse on which someone was riding.