Abu Uthman al-Nahdi (may Allah have mercy on him) said: I was with Sayyiduna Salman al-Farisi (may Allah be pleased with him) under a tree. He took hold of one of its dry branches and shook it until its leaves fell, then said: Ask me why I am doing this. I said: Why are you doing it? He said: The Messenger of Allah (peace and blessings be upon him) did the same. I was with him under a tree, and he (peace and blessings be upon him) took hold of one of its dry branches and shook it until its leaves fell, then said: "O Salman! Will you not ask me why I am doing this?" I said: Why are you doing it? He said: "When a Muslim performs ablution and performs it well, then prays the five prayers, his sins fall away just as these leaves have fallen." Then he (peace and blessings be upon him) recited this verse: "Establish the prayer at the two ends of the day and in some hours of the night. Indeed, good deeds wipe out evil deeds. That is a reminder for those who remember." [Surah Hud: 114]
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6126