This Salah is not an actual Salah                           .   Salatut Tasbih in Hadith Muhammad said to his uncle Abbas that, "Uncle, If you can you may say salatul tasbih once in a week, if you can't, you may say it once in a month, or once in a year, else once in your life. This salah helps to receive forgiveness from your life's smaller, bigger, voluntary, involuntary, newer, older, hidden, expressed and all kinds of sins. (Graded weak)
Salatul Tasbih (صلاة تسبيح) is better known as Tasbih's Salat. Here, Tasbih means "Subhanallahi wal Hamdulillahi, wala Ilaha Illallahu, wallahu Akbar". In which salat those tasbihs are read, that kind of salat is known as Salatul Tasbih. It is not like the mandatory five period of salats, but a special kind of salat. Muhammad advised his Ummahs to pray this salat for at least one time in their life. Way to perform Salatut Tasbih This special salat consists of four rakats.which are performed the same way as the other usual rakats, but the only difference is that this salat has 300 tasbihs in it. Which are performed the same way as the usual rakats but the only difference is to recite 75 tasbihs per rakat that is 300 tasbihs in total. Actual steps to perform the Salatut Tasbih 1) Once you stand for this special Salah, and after reciting the Sana( سُبْـحانَكَ اللّهُـمَّ وَبِحَمْـدِكََ وَتَبارَكَ اسْمُـكَ وَتَعـالى جَـدُّكَ وَلا إِلهَ غَيْرُك) recite this tasbih (Subhanallahi wal Hamdulillahii, wala Ilaha Illallahu, wallahuu Akbar) 15 times 2) After reciting Surah Fatiha and some other Surah, recite this tasbih 10 times 3) During Rukuh, after saying prescribed glorifications (subhana rabal azeem), recite the tasbih 10 times 4) After standing up from Rukuh, recite the tasbih 10 times 5) In the first Sajda after glorifications (subhana rabal aala), recite the tasbihh 10 times 6) In the Jalsa (time between the Sajda) recite the tasbih 10 times 7) Again recite the tasbih 10 times in the second sajdah Repeat the same thing in 2nd 3rd and 4th rakat in exactly the same way as in first one . Counting of tasbihs in one ratat = (15+10+10+10+10+10+10)= 75 In four rakats = 75*4 = 300 Salatut Tasbih in Hadith Muhammad said to his uncle Abbas that, "Uncle, If you can you may say salatul tasbih once in a week, if you can't, you may say it once in a month, or once in a year, else once in your life. This salah helps to receive forgiveness from your life's smaller, bigger, voluntary, involuntary, newer, older, hidden, expressed and all kinds of sins. 
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This Salah is not an actual Salah
Salatul Tasbih (صلاة تسبيح) is better known as Tasbih's Salat. Here, Tasbih means "Subhanallahi wal Hamdulillahi, wala Ilaha Illallahu, wallahu Akbar". In which salat those tasbihs are read, that kind of salat is known as Salatul Tasbih. It is not like the mandatory five period of salats, but a special kind of salat. Muhammad advised his Ummahs to pray this salat for at least one time in their life.
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Way to perform Salatut Tasbih
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This special salat consists of four rakats.which are performed the same way as the other usual rakats, but the only difference is that this salat has 300 tasbihs in it.
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Which are performed the same way as the usual rakats but the only difference is to recite 75 tasbihs per rakat that is 300 tasbihs in total.
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Actual steps to perform the Salatut Tasbih
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1) Once you stand for this special Salah,
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and after reciting the Sana( سُبْـحانَكَ اللّهُـمَّ
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وَبِحَمْـدِكََ وَتَبارَكَ اسْمُـكَ وَتَعـالى جَـدُّكَ وَلا إِلهَ غَيْرُك)
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recite this tasbih (Subhanallahi wal
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Hamdulillahii, wala Ilaha Illallahu,
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wallahuu Akbar) 15 times
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2) After reciting Surah Fatiha and some
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other Surah, recite this
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tasbih 10 times
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3) During Rukuh, after saying prescribed
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glorifications (subhana rabal azeem),
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recite the tasbih 10 times
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4) After standing up from Rukuh, recite the
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tasbih 10 times
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5) In the first Sajda after glorifications
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(subhana rabal aala), recite the
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tasbihh 10 times
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6) In the Jalsa (time between the Sajda)
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recite the tasbih 10 times
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7) Again recite the tasbih 10 times in the
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second sajdah
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Repeat the same thing in 2nd 3rd and 4th rakat in exactly the same way as in first one
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Counting of tasbihs in one ratat = (15+10+10+10+10+10+10)= 75
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In four rakats = 75*4 = 300
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(Graded weak)