The Imamis consider salat performed in a usurped place and usurped clothing as invalid (batil) provided it is done voluntarily and with the knowledge of the usurpation. The other schools observe: The salat performed in a usurped place is valid, though the person performing it will have sinned, since the prohibition does not relate directly to salat; rather, it relates to dispensations (of property). Their position in this regard is the same as in the case of usurped clothing.
What a great distance between this opinion of the four schools the a usurper’s salat is valid in usurped property, and the opinion of the Zaydiyah that because of the prohibition on the use of anything usurped, it is not valid even for the true owner to perform salat in his property as long as it remains usurped.
The Imami view represents a middle position, because they consider as valid the salat of the true owner and anyone whom he permits, and regard as invalid (batil) the salat of the usurper and anyone whom the owner has not granted permission. The Imamis also permit salat in vast stretches of (owned) land which are either impossible or difficult for people to avoid, even if the permission of the owner has not been acquired.
The four Sunni schools observe: The place should be free from both wet and dry najasah (impurity). The Shafi’is overdo by saying: The taharah of all that which touches and comes into contact with the body or clothes of the musalli is wajib.
Therefore, if he rubs himself against a najis wall or cloth or holds a najis object or a rope laying over najasah, his salat will be invalid (batil). The Hanafis require only the location of the feet and the forehead to be tahir. The Imamis restrict it to the location of the forehead, i.e. the place of sajdah. As to the najasah of other locations, the salat will not be batil unless the najasah is transmitted to the body or clothing of the musalli (the person performing salat).
The Hanafis and the Imamis require the place to be stationary; hence it is not valid in their opinion to perform salat while riding an animal or something that swings back and forth, except out of necessity, because one who has no choice will perform salat in accordance with his capacity.
The Shafi’is, Malikis and Hanbalis observe: Salat performed on a mount is valid even during times of peace and despite the ability to perform it on the ground, provided it is performed completely and meets all the requirements.
The Imamis, Shafi’is and Hanafis state: It is valid to perform salat, faridah or nafilah, inside the Ka’bah.
The Malikis and the Hanbalis say: Only nafilah, not faridah, is valid therein.
A group of Imami legists observe: If a man and a woman perform salat in a single place so that she is either in front of him or beside him, and there is neither any screen between them nor does the distance between the two exceed 10 cubits, the salat of the one who starts earlier will not be invalid (batil), and if both start simultaneously, the salat of both will be batil.
The Hanafis say: If the woman is in front or beside a man, the salat will be invalid (batil) if performed in a single place with no screen at least a cubit high between them, the woman has sex appeal, her shanks and ankles are adjacent to his, the salat is not a funeral prayer, and the salat is being jointly performed, i.e. either she is following him or both are following a single imam.
The Shafi’is, the Hanbalis and most Imamis are of the view that the salat is valid, though the manner of performance is makruh.
The schools concur that the place where the forehead is placed during prostration should be stationary and should not be inordinately higher than the location of the knees (during sajdah). They differ regarding that on which sajdah is valid.
The Imamis state: It is valid to perform sajdah only on earth and those things which grow on it and are not used for food or clothing. Therefore, a person cannot perform sajdah on wool, cotton, minerals and that which grows on the surface of water, for water is not earth.
They permit sajdah on paper because it is made of a material which grows on earth. They argue their position by pointing out that sajdah is an ‘ibadah prescribed by the Shari’ah that depends for its particulars on textual evidence (nass). The legists of all the schools concur regarding the validity of sajdah on earth and that which grows on it, thus Imamis restrict it to that because there is certainty. They offer as further evidence these traditions of the Prophet (S):
لا تتم صلاة أحدكم حتى يتوضأ كما أمر الله، ثُمّ يسجد ممكناً جبهته مِن الأرض
The salat of any of you will not be valid unless he performs wudu’ as instructed by God and then performs sajdah by placing his forehead on the earth.
خلقت الأرض مسجداً وطهوراً
The earth has been created a masjid (a place for performing sajdah) and a purifier.
Khabbab says: "We complained to the Prophet (S) regarding the excessive heat of sun-baked ground on our foreheads, but he did not accept our complaint."
Had it been valid to perform sajdah on carpets, why would they have complained?
Imamis permit sajdah on cotton and linen in the case of idtirar (emergency).
The four schools observe: It is valid to perform sajdah on anything, including even a part of one’s turban, provided it is tahir. Rather, the Hanafis permit sajdah on one’s palm even without an emergency, though it is considered as makruh.