Abu Ghalib narrates: I heard Sayyiduna Abu Umamah (may Allah be pleased with him) say: "No Muslim hears the call to prayer (adhan) and gets up to perform ablution (wudu) except that he is forgiven with the first drop of that water that falls from his palm; and after that drop Allah forgives all his past sins. Then he stands for his prayer, and it is nafl (additional) for him." I said: O Abu Umamah, did you hear this from the Messenger of Allah (peace and blessings be upon him)? He said: "By the One who sent him (peace and blessings be upon him) as a bearer of glad tidings and a warner, (I heard it) not once, not twice, not three times, not four times, not ten times (but even more than that)." And he gestured by closing (the fingers of) his hand again and again.
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 8030