It is narrated from Sayyiduna Salman (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "A man said: 'Alhamdu lillahi kathira' (All praise is for Allah, abundantly), and the angel considered it a very great matter to record it (because of the vastness of its reward), and he referred back to his Lord, the Mighty and Majestic, about it. He was told: 'Write it just as My servant said it, that is, kathira (abundantly).'"
Hadith Referenceالمعجم الأوسط / باب الألف / 2061
Hadith Gradingمحدثین:فيه يوسف بن عبد الملك الواسطي لم يُعرف، وبقية رجاله ثقات
Hadith Takhrij«قال الهيثمي: وفيه يوسف بن عبد الملك الواسطي ولم أعرفه وبقية رجاله ثقات «مجمع الزوائد ومنبع الفوائد، ج 10، ص 96»»