Ibn al-Daylami (may Allah be pleased with him), who was the nephew (sister's son) of the Negus and used to serve the Prophet (peace and blessings be upon him), narrates that the Messenger of Allah (peace and blessings be upon him) said: "Whoever recites 'Qul huwa Allahu ahad' (Say: He is Allah, the One) one hundred times, in prayer or outside it, Allah writes for him freedom from the Fire."
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15943