The Forty Hadith of Imam al-Nawawi.
On the authority of Abu Muhammad, 'Abdullah ibn 'Amr ibn al-'As (may Allah be pleased with them both), who said:
The Messenger of Allah (peace and blessings of Allah be upon him) said:
"None of you truly believes until his desires conform to what I have brought."
This hadith indicates the perfection of faith,
and that the true mark of sincere faith
is for a Muslim to make his desires and inclinations subordinate to what the Prophet (peace be upon him) brought
by way of guidance and divine law,
giving precedence to obedience to Allah over the desires of the self.
For the more a person aligns his choices and desires with the Sacred Law,
the closer he is to achieving complete faith.
The hadith also nurtures self-discipline and the struggle against one's base desires,
so that whim does not govern human conduct,
but rather the Muslim's standard remains divine revelation and faithful following.