Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) narrates: the Prophet (peace and blessings be upon him) came out in the winter season while the leaves were falling. the Prophet (peace and blessings be upon him) took hold of a branch of a tree, and its leaves began to fall. He (peace and blessings be upon him) said: "O Abu Dharr!" I said: "O Messenger of Allah, here I am at your service." the Prophet (peace and blessings be upon him) said: "When a Muslim servant offers the prayer, seeking by it the pleasure of Allah Almighty, his sins fall away from him just as these leaves are falling from this tree."
Ahmad recorded it, and its narrators are thiqat (trustworthy).