It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) passed by a man who was reciting 'Qul huwa Allahu ahad' (Say: He is Allah, the One), and he (peace and blessings be upon him) said: "He has made (Paradise) obligatory (for himself); Paradise has become due for him."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7835