Sayyiduna Zaid bin Thabit (may Allah be pleased with him) said: We were commanded to say «سبحان الله» 33 times, «الحمد لله» 33 times, and «الله اكبر» 34 times after every prayer. Then a man from among the Ansar was told in a dream: Has your Prophet commanded you to say tasbih 33 times, tahmid 33 times, and takbir 34 times after every prayer? He said: Yes. So he (the one in the dream) said: Say them 25 times each, and say «لا اله الا الله» 25 times. When this dream was mentioned to the Prophet Muhammad (peace and blessings be upon him), he said: "Do so."
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1392