It is narrated from Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever says: 'There is no true god but Allah, alone, without partner; His is the dominion and to Him belongs all praise, and He has power over all things,' it will be for him equal to freeing one or two slaves."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4002