The Messenger of Allah ﷺ said, "Whoever says after the dawn prayer, before he bends his legs, 'There is no god but Allah alone, with no partner. To Him belongs the dominion, and to Him belongs all praise. He gives life and causes death. In His hand is all good, and He has power over all things,' one hundred times, will be on that day the best of the people of the earth, except for one who says the same as he said or adds to what he said."
قال رسول الله ﷺ: من قال في دبر صلاة الغداة: لا إله إلا الله وحده لا شريك له، له الملك، وله الحمد، يحيي ويميت بيده الخير وهو على كل شيء قدير مائة مرة قبل أن يثني رجليه كان يومئذ أفضل أهل الأرض إلا من قال مثل ما قال أو زاد على ما قال.
Tabarani related it in Kabir (8/336), and in Awsat (4656, Majma Bahrain), and Ibn Sunni in Amal al-Yawm wal-Layla (143), all of them via Abdul-Samad bin Abdul-Warith, from Adam bin Hakam, who said, Abu Ghalib told us, from Abu Umama, and he related it. Its chain of transmission is hasan because of Adam bin Hakam, who is Basri, and Abu Ghalib, for both of them are considered narrators whose hadith is hasan. Ibn Hajar also graded it hasan in Nataij Afkar.Something similar in meaning was related from Abu Dharr, that the Messenger of Allah ﷺ said, "Whoever, after the prayer of Fajr, while still in his sitting position before he speaks, says, 'There is no god but Allah, alone, without partner, His is the dominion and His is the praise, He gives life and causes death, in His hand is all good, and He has power over all things,' ten times, will have ten good deeds recorded for him, ten bad deeds erased from him, and he will be raised ten degrees. That entire day he will be under protection from everything disliked and guarded from Satan, and no sin will be able to reach him that day except shirk against Allah."Tirmidhi related it (3474), and Nasai in Amal al-Yawm wal-Layla (127), both of them via Shahr bin Hawshab, from Abdul-Rahman bin Ghanm, from Abu Dharr, and he related it. Tirmidhi said, "A hasan sahih gharib hadith," and in some copies, "hasan gharib."I say, Shahr bin Hawshab is, in my view, a narrator whose hadith is hasan so long as his error has not been established, but he was inconsistent regarding this hadith, and it has been related from him in many different forms, which Daraqutni laid out in Ilal (6/247–249), then said, It appears that this inconsistency comes from Shahr. And Allah knows best.Dubur means "immediately following" the prayer.