Complete Sincerity on Prophets
Another indispensable characteristic is sincerity, which in this context means “purity of intention, to do everything solely for the sake of God.
” We are told to worship God sincerely: They were commanded only to serve God, making the religion His sincerely, men of pure faith, and to perform the prayer, and pay the alms (98:5). God also mentions sincerity as the foremost attribute of the Prophets: And mention in the Book Moses; he was made sincere, and he was a Messenger, a Prophet (19:51).
We worship God only because we are His servants and He has told us to do so. Obeying Him allows us to secure His approval and be rewarded in the Hereafter. Said Nursi, the great twentieth-century Turkish thinker, said:
“Do what you do only for God’s sake, start for God’s sake, work for God’s sake, and act within the sphere of God’s good approval.” 
God’s Last Prophet worshipped God so sincerely that people could say:
“No one can remain as humble as he was at the beginning of his career or quest after attaining its height. Muhammad was an exception to this.”
He is so great and sublime that we still stand out of respect for him, although he used to warn his Companions:
“When I come upon you, don’t stand up as the Persians do (for their elders).” 
Although his Companions had complete respect for him, he considered himself a poor slave of God. On the day he conquered Makka, he was the same as when he humbly had begun his mission. At the outset of his mission, he would sit and eat with the poor and slaves. As he entered Makka in triumph, he rode a mule in such deep submission and humility before God that his forehead touched its packsaddle. He was prostrating before God and taking refuge in Him from being a tyrannical, haughty conqueror.
God’s Messenger had one intention: to please God and worship Him sincerely. He worshipped Him at a level of perfect goodness and sincerity, as he himself stated in a famous Tradition:
“Perfect goodness or virtue is to worship God as if you were seeing Him, and while you see Him not, yet truly He sees you.” 
By M. Fethullah Gulen
 Bediuzzaman Said Nursi, The Words, The First Word, 5.
 Abu Dawud, Adab, 152; Ibn Hanbal, 5:253.
 Bukhari, Iman, 47; Muslim, Iman, 5:7.