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Hisn al-Muslim (Fortress of the Muslim) 254
قَالَ صلى الله عليه وسلم مَنْ قَالَ: سُبْحَانَ اللَّهِ وَبِحَمْدِهِ فِي يَوْمٍ مِائَةَ مَرَّةٍ حُطَّتْ خَطَايَاهُ وَلَوْ كَانَتْ مِثْلَ زَبَدِ الْبَحْر)).
(Whoever says:(How perfect Allah is and I praise Him.) a hundred times during the day, his sins are wiped away, even if they are like the foam of the sea.)
Cited in Hisn al-Muslim (Fortress of the Muslim) (No. 254).