5. Sajdah: Each rak'at has two sajdah, both taken together are one rukn. Seven things are wajib in a sajdah:
1. One should prostrate so low that his forehead and feet are in one level.
2. Seven parts of the body must be resting on the ground. These are the forehead, the two palms, the two knees and the toes of both feet.
3. There are some special rules about the place of sajdah;-
4. It must be either earth; or
5. Anything growing from earth, provided it is from those things which are not eaten nor worn.
Therefore, sajdah is not allowed on clothes or fruits or edible vegetables, or on such a thing which does not come under the term 'earth' viz., diamond or gold etc., or does not come under the term vegetation viz., ash or coal.
Also, sajdah is not correct on hide or skin, because it does not grow from the earth; nor is it allowed on carpets made of wool, cotton, jute or silk, because wool and silk do not grow from earth and cotton and jute are used in clothes.
Sajdah on paper is allowed.
Highest preference has been given for performing sajdah on the earth from a specified area in Karbala. That earth is called 'khak al-shifa', readymade tablets of which are available and are called 'muhr, or 'turbat' or 'sajdah-gah: in different languages.
The muhr must be clean. Dirty tablets are not allowed in prayers. Also, the size of muhr should not be less than your own thumb.
Bibi Fatimah al-Zahra’ had made 'tasbih' from the earth taken from the grave of Hazrat Hamza (A.S..)
I am sorry to note that in many mosques very few 'tasbihs' contain correct number of beads. Before using a tasbih you should count the beads to make sure that it is correct.
The arrangement of the beads should be: 33 round beads + one marker + 32 round beads + one marker + 33 round beads.
If there is nothing upon which sajdah is allowed, or there is so much cold or heat that a person cannot put his forehead upon the earth, then, he may perform sajdah upon his clothes. If there are no clothes then, as a last resort, it is allowed to perform sajdah upon the back of his hand. Normally, this condition is not common, and the person praying should not do sajdah upon his clothes or the back of his palm. Sometimes it is seen that people do their sajdah upon their hands or nails, even while praying in the Masjid.
Their prayer is invalid (batil), without any doubt. Remember that the mats are made from a fiber which is neither eaten nor worn and it is quite in order to do sajdah on them, especially if your forehead rests upon an uncolored portion. Likewise, you may do sajdah on any stone (not precious stones); so you can do sajdah on real (but not on artificial) marble. Cement and lime are made from burnt stones; therefore a cemented floor or floor covered with lime cannot be used for sajdah. Likewise, sajdah is not allowed on earthenware, after it has been treated by fire.
4. To recite dhikr of sajdah, i.e. Subhanallah (three times) or Subhana Rabbiyal A’ala wa bihamdih (Glory and Praise be to my Lord Cherisher, the High) (once).
5. To remain motionless-during Dhikr of sajdah.
6. Not to raise any of the seven parts (mentioned in No.2) till the recitation of dhikr is over.
7. To raise the head first and sit down after first (and even second) sajdah.
"It is haraam in Islamic shari’ah to do sajdah to anyone except Allah. Some ignorant people put their forehead in front of the graves of Imams (A.S.). If they have a clear intention to do sajdah of thanks (sajdah al-shukr) for Allah, it is alright. Otherwise, it is haraam."