theclearpath.com

"And whosoever submits his face (himself) to Allaah [i.e.(follows Allaah's Religion of Islaamic Monotheism), worships Allaah (Alone) with sincere Faith in the (1) Oneness of His Lordship,(2) Oneness of His worship, and (3) Oneness of His Names and Qualities], while he is a Muhsin (good-doer i.e, performs good deeds totally for Allaah's sake without any show-off or to gain praise or fame etc, and does them in accordance with the Sunnah of Allaah's Messenger Muhammad sal-Allaahu 'alayhe wa sallam), then he has grasped the most trustworthy hand-hold [La Ilaaha ill-Allaah (none has the right to be worshipped but Allaah)], And to Allaah return all matters for decision." [Luqmaan (31):22]

Narrated 'Abdullah bin 'Abbas:

I was informed by Abu Sufyan that Heraclius said to him, "I asked you whether they (followers of Muhammad) were increasing or decreasing. You replied that they were increasing. And in fact, this is the way of true Faith till it is complete in all respects. I further asked you whether there was anybody, who, after embracing his (the Prophets) religion (Islam) became displeased and discarded it. You replied in the negative, and in fact, this is (a sign of) true faith. When its delight enters the heart and mixes with them completely, nobody can be displeased with it." [The Book of Faith Volume 1, Book 2, Hadeeth 48]