The Prophet (sallallaahu 'alayhi wa sallam) said,
"There are three qualities whoever has them, will taste the sweetness of Imaan: To love Allah and His Messenger (sallallaahu 'alayhi wa sallam) more than anyone else; to love a slave (of Allah) only for (the sake of) Allah; and to abhor returning to infidelity after Allah has saved him from it as he would abhor to be thrown into the fire (of Hell)".
[Al-Bukhari and Muslim].