The Messenger of Allah ﷺ said, "Whoever says, 'There is no god but Allah alone, with no partner. To Him belongs the dominion and to Him belongs all praise, and He has power over all things,' ten times, is like one who has freed four souls from the descendants of Ismail."
أن رسول الله ﷺ قال: من قال: لا إله إلا الله وحده لا شريك له، له الملك وله الحمد وهو على كل شيء قدير عشر مرات كان كمن أعتق أربعة أنفس من ولد إسماعيل.
Bukhari narrated it in the Book of Supplications (6404), and Muslim in the Book of Remembrance and Supplication (2693), both from the hadith of Umar bin Abu Zaida, from Abu Ishaq, from Amr bin Maymun, who said, "Whoever says, 'There is no god but Allah'..." and so on to the end. Umar (Ibn Abu Zaida) said, Abdullah bin Abu Safar told us, from Shaybi, from Rabi bin Khuthaym, with the same account. He said, "I asked Rabi, 'From whom did you hear it?'" He said, "From Amr bin Maymun." He said, "So I went to Amr bin Maymun and asked him, 'From whom did you hear it?'" He said, "From Ibn Abu Layla." He said, "So I went to Ibn Abu Layla and asked him, 'From whom did you hear it?'" He said, "From Abu Ayub Ansari, who related it from the Messenger of Allah ﷺ."Ahmad also narrated it (23546) from Yazid (that is, Ibn Harun), Dawud (that is, Ibn Abu Hind) informed us, from Amir (that is, Shaybi), from Abdul-Rahman bin Abu Layla, from Abu Ayub, with a similar wording. It contains, "It will count for him as the equivalent of freeing ten slaves, or one slave." Its chain of transmission is sahih.