"The Messenger of Allah ﷺ said: 'Whoever says the tasbih one hundred times following the morning prayer, and the tahlil one hundred times, he will be forgiven his sins even if they are like the foam of the sea.'" (Using translation from Nasāʾī 1354)  

قَالَ رَسُولُ اللهِ ﷺ «مَنْ سَبَّحَ فِي دُبُرَ صَلَاةِ الْغَدَاةِ مِائَةَ تَسْبِيحَةٍ وَهَلَّلَ مِائَةَ تَهْلِيلَةٍ غُفِرَ لَهُ ذُنُوبُهُ وَلَوْ كَانَتْ مِثْلَ زَبَدِ الْبَحْرِ»  

[Machine] The Messenger of Allah ﷺ said, "Whoever says tasbih (glorification of Allah) 100 times after Fajr prayer and tahleelah (proclaiming the oneness of Allah) 100 times, his sins will be forgiven, even if they are as abundant as the foam of the sea." Abu Abdur-Rahman Ya'qub bin 'Ata bin Abi Rabah said, "Weak narration." And Abdullah bin Tawus is trustworthy and reliable, and Abdullah bin Sa'id bin Jubayr is trustworthy and reliable, and Ikrimah, the freed slave of Ibn Abbas, is trustworthy and one of the most knowledgeable people. Amr bin Dinar narrated it from Jabir bin Zaid.  

قَالَ رَسُولُ اللهِ ﷺ «مَنْ سَبَّحَ فِي دُبُرِ صَلَاةِ الْغَدَاةِ مِائَةَ تَسْبِيحَةٍ وَهَلَّلَ مِائَةَ تَهْلِيلَةٍ غُفِرَ لَهُ ذُنُوبُهُ وَإنْ كَانَتْ مِثْلَ زَبَدِ الْبَحْرِ» قَالَ أَبُو عَبْدِ الرَّحْمَنِ يَعْقُوبُ بْنُ عَطَاءِ بْنِ أَبِي رَبَاحٍ ضَعِيفٌ وَعَبْدُ الْوَهَّابِ بْنُ مُجَاهِدٍ مَتْرُوكُ الْحَدِيثِ وَعَبْدُ اللهِ بْنُ طَاوُسٍ ثِقَةٌ مَأْمُونٌ وَعَبْدُ اللهِ بْنُ سَعِيدِ بْنِ جُبَيْرٍ ثِقَةٌ مَأْمُونٌ وَعِكْرِمَةُ مَوْلَى ابْنِ عَبَّاسٍ ثِقَةٌ مِنْ أَعْلَمِ النَّاسِ قَالَهُ عَمْرُو بْنُ دِينَارٍ عَنْ جَابِرِ بْنِ زَيْدٍ