The love of the companions of the Prophet , such as Abu Hurayra is a sign of belief, according to the exact wording of the Prophet that Allah make Abu Hurayra beloved to the believers.

Abu Hurayra gave the following account of his mother's conversion:

I came to the Prophet weeping one day and said: "O Messenger of Allah, I have been inviting my mother to Islam and she has been refusing. Today I asked her again, and she said something about you which I hated to hear. Ask Allah to guide Abu Hurayra's mother!" Whereupon the Prophet said: "O Allah! Guide Abu Hurayra's mother."
   Then I returned home cheered up by the Prophet's supplication. When I arrived at the door of the house I found it closed. Hearing my footsteps, my mother said: "Abu Hurayra, do not come in yet." I could hear the sound of water. She washed herself and wore her robe (dir') and headcover (khim_r) then she opened the door and said: "Abu Hurayra! I bear witness that there is no God but Allah and that Muhammad is Allah's servant and messenger!"
   I returned at once to the Prophet , weeping for joy, and said to him: "O Messenger of Allah, good news! Allah has answered your request and guided my mother!" He glorified and praised Allah, thanking Him and saying good things. I said: "O Messenger of Allah! Ask Allah that He make me and my mother beloved to his believing servants and that He make them beloved to us."
   The Prophet said: "O Allah! Make Your little servant here - meaning Abu Hurayra - and his mother beloved to Your believing servants, and make the believers beloved to the two of them." Not one believer is brought into existence who hears about me without seeing me except he loves me.

Narrated by Muslim and Ahmad. Also Ibn Hajar in al-Isaba (7:435, 7:512) and others.

This hadith is similar to another sound hadith of the Prophet addressing the Commander of the Believers 'Ali ibn Abi Talib (r):

"None loves you except a believer, and none hates you except a hypocrite." Narrated by Muslim, al-Nasa'i, and Ahmad