Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) narrates: When the Prophet (peace and blessings be upon him) came to Madinah, he stayed with me. He said: "O Abu Ayyub, shall I not teach you?" I said: "Yes, O Messenger of Allah." The Prophet (peace and blessings be upon him) said: "Any servant who recites these words in the morning: 'La ilaha illallahu wahdahu la sharika lahu, lahul-mulku wa lahul-hamdu'
(There is no deity except Allah Almighty; He alone is the deity, He has no partner; to Him alone belongs the dominion and to Him alone belongs all praise)
(the Prophet, peace and blessings be upon him, says:) then because of it Allah Almighty records ten good deeds for that person and erases ten of that person's sins; these words will be, before Allah Almighty, equal to freeing 10 slaves, and they will be a protection from Satan until the evening. And whoever recites them in the evening will also obtain the like of it (that is, the same reward)."
Ahmad recorded it, and al-Tabarani recorded something similar.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16985