مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ٢٣١ - SAJDATAYN(TWO PROSTRATIONS)

e.g. if he joins his chest and belly with the ground or stretches his feet, he should, on the basis ofrecommended precaution, offer the prayers again, notwithstanding the fact that the seven limbs mentioned above touch the ground. However, if he stretches his feet so muchthat it cannot be said that he is performing prostration, his prayers is void.
١٠٧٤. The mohr (tablet for prostration) or other thing on which a person performs prostration should be pure. However, if, for example, he places the mohr on impurecarpet, or one side of the mohr is impure and he places his forehead on its pure side, there is no harm in it.
١٠٧٥. If there is a sore or some other similar thing in the forehead of a person he should, if possible, offer prostration on the healthy part of his forehead. Andif this is not possible he should dig the earth and place the sore in the cavity and as much of the healthy part of his forehead on the earth as is sufficient forprostration.
١٠٧٦. If the sore or wound has covered the entire forehead of a man, he should, on the basis of precaution, perform prostration with one of the two sides offorehead and chin, even possible he should do it with chin only. And if it is not possible to perform prostration even with his chin he should make a sign for prostration.
١٠٧٧. If a person cannot make his forehead reach the ground he should bend as much as he can, and should place the mohr or any other thing on which it is lawful toperform prostration, on something which is high, and should place his forehead on it in such a way that it may be said that he has performed prostration. He should howeverplace the palms of his hands, and his knees and toes on the ground as usual.
١٠٧٨. If the person offering prayers cannot procure something high on which he place the