What Salatul Tasbeeh isA gift the Prophet ﷺ gave his uncle
Ibn Abbas reports that the Prophet ﷺ said to al-Abbas: “O Abbas, my uncle, shall I not give you something, shall I not grant you something?” He then taught him four rakats in which the words of glorification are said 75 times in every rakat, and said that if he prayed them, Allah would forgive his sins: the first and the last, the old and the new, the mistaken and the deliberate, the small and the great, the hidden and the open (Abu Dawud 1297, Ibn Majah 1387).
Then he made it easy to keep: pray it every day if you can; if not, every Friday; if not, once a month; if not, once a year; and if not, once in your life.
The prayer is called Salatul Tasbeeh (also written Salat al-Tasbih, Salatul Tasbih or Tasbeeh Namaz) because of the tasbih at its heart: Subhanallah, walhamdulillah, wa la ilaha illallah, wallahu akbar. These are the four phrases the Prophet ﷺ called the most beloved words to Allah (Muslim 2137).