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 (6404) and Muslim (2693) both narrated it through the hadith of Umar bin Abu Zaida, from Abu Ishaq, from Amr bin Maymun, who said, "Whoever says, There is no god but Allah... etc." Umar (Ibn Abu Zaida) said, Abdullah bin Abu Safar told us, from Shaybi, from Rabi bin Khuthaym, with the same wording. I said to Rabi, "From whom did you hear it?" He said, "From Amr bin Maymun." So I went to Amr bin Maymun and said, "From whom did you hear it?" He said, "From Ibn Abu Layla." So I went to Ibn Abu Layla and said, "From whom did you hear it?" He said, "From Abu Ayub Ansari, who narrated it from the Messenger of Allah ﷺ."