This is because it is established that the Prophet, peace and blessings be upon him, prayed upon a khumrah (a small palm-leaf mat). (1)

A khumrah is a small mat woven from palm leaves, large enough only for the worshipper’s forehead and palms. Thus, barriers fall into three categories:

1. A barrier consisting of one of the limbs used in prostration. Prostrating upon this is prohibited, and the prostration is invalid.

2. A barrier that is not one of the limbs used in prostration but is attached to the worshipper. This is disliked; if it is done, the prostration is still valid, though disliked.

3. A separate barrier. There is nothing wrong with this. However, the scholars said that it is disliked for a person to reserve something upon which to prostrate exclusively for his forehead.

They explained this by saying that it resembles the practice of the Rafidah in their prayer. The Rafidah treat this as a religious observance: they pray upon a piece of hardened clay, like earthenware, fashioned from what they call al-Najaf al-Ashraf, placing only their foreheads upon it. Thus, at the entrances to their mosques, one finds cabinets filled with these stones; when a person wishes to enter the mosque, he takes a stone upon which to prostrate. Some of them do this because they believe that prostration is permissible only upon something of the same kind as the earth. Accordingly, they hold that it is not permissible to prostrate upon bedding, even if it is made of woven palm leaves—despite its being established that the Prophet, peace and blessings be upon him, prostrated upon woven palm leaves, as mentioned in the hadith of Anas, when he washed for the Prophet, peace and blessings be upon him,