It has been authentically confirmed on the authority of Anas (رضي الله عنه) that the Prophet (صلى الله عليه وسلم) said: “Three characteristics allow one to taste the sweetness of īmān: Allāh and His Messenger are more beloved to him than anything. He loves a person for no reason other than Allāh. He hates to apostate from his religion as much as he hates to be cast into the Fire.”
Narrated by al-Bukhārī: 21 and Muslim 43

Imām al-Qurṭubī comments:

This ḥadīth proves that the type of love one harbours for a believer—which is closely connected to tasting the sweetness of īmān—is only love that is solely and sincerely for the sake of Allāh the Most High, unadulterated by any worldly goals or human ambitions. This is because the love one feels for the believers in connection to these things will immediately be severed once that purpose is fulfilled or he has completely lost hope in its attainment. Rather, truly loving a believer is a continuous, perpetual state of being, whether one’s personal goals or purposes are achieved or not. It is due to the fact that most of the love that occurs is actually for personal reasons, therefore very few people are able to taste the sweetness of īmān. It may even border on complete obsoletion. Especially, in these times wherein the signs and characteristics of true īmān have generally been wiped away from most people. Truly loving the believer is, undoubtedly, only accomplished with sincerity and righteous intentions.

Source: Al-Mufhim: 214-215
Translated by: Riyāḍ al-Kanadī