مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ١٥٥ - THINGS ON WHICH TAYAMMUM MAY BE PERFORMED

if performed in a state of forgetfulness or negligence, is in order. However, if a person usurps something himself and forgets that he has usurped it and performs tayammum on it or if he usurps a property and forgets that he has usurped it, and places the thing on which he is performing tayammum on that property, or performs tayammum in the space of that property, the same orders apply to him which apply to a person who performs an act intentionally.
٧٠٥. If a person is imprisoned in a usurped place and both the water and earth of that place are usurped he should offer prayers with tayommum.
٧٠٦. The thing on which a person is performing tayammum should if possible, have, on the basis of precaution dust which should stick to the hands, and after striking hands on it, he should shake them so that the dust may fall off.
٧٠٧. It is abominable to perform tayammum on the earth of a pit, or a path or the saline earth on which a layer of salt has not settled. In case, however, a layer of salt has settled on the earth, performance of tayammum on it is void.

METHOD OF PERFORMING TAYAMMUM IN LIEU OF BATH OR ABLUTIONS
٧٠٨. The following ٤ things are obligatory regarding tayammum which is performed in lieu of taking ceremonial bath or performing ablutions (i) Intention (ii)Striking both the palms on the object on which tayammum is valid. (iii) Wiping or stroking with the palms of both the hands the entire forehead and its two sides commencing from the spot where the hair of ones head grow up to the eyebrows and above the nose and as a precautionary measure the hands should also stroke the eyebrows. (iv) The palm of the left hand should be wiped on the entire back of the right hand and thereafter the palm of the right hand should wipe the entire back of the left hand.