The prayer rug is a small rug laid down for the ritual prayer of Islam, and its purpose is simple and practical: to ensure a clean surface for prostration.
Cleanliness, not obligation
Ritual purity of the place of prayer is required, and the prayer rug guarantees a clean spot for the forehead and hands in prostration wherever the worshipper happens to be, which is its whole function. It is not itself required, since any clean ground will serve, and the Prophet is reported to have prayed on the bare earth and on a simple mat, so the rug is a convenience and a mark of respect rather than a necessity. Its portability lets the five daily prayers be performed anywhere in a state of cleanliness.
Design and direction
Prayer rugs very often carry a woven arch or niche, the mihrab motif, which the worshipper points toward the direction of Mecca, so the design itself helps orient the prayer, and the patterns are typically non-figural in keeping with the avoidance of images in the setting of worship. The rugs are among the most widespread and finely made of Islamic textiles, and a well-made prayer rug may be a valued possession and a gift, but the object remains subordinate to its function. It is the clean ground for prostration made portable, which is why it accompanies the believer rather than belonging to a building.