Abu Ayyub Al-Ansari (May Allah be pleased with him) reported:
'La ilaha illallahu, wahdahu la sharika lahu, lahulmulku wa lahulhamdu,
wa Huwa 'ala kulli sha'in Qadir
(there is no true god except Allah. He is One and He has no partner with Him. His is the sovereignty and His is the praise, and He is Omnipotent),' he will have a reward equal to that for freeing four slaves from the progeny of Prophet Isma'il."
[Al- Bukhari and Muslim].