Sahih Bukhari Volume 4, Book 54, Hadith Number 431.

Narated By Abu Huraira : The Prophet said, “If Allah loves a person, He calls Gabriel saying, ‘Allah loves so and-so; O Gabriel! Love him.’ Gabriel would love him and make an announcement amongst the inhabitants of the Heaven. ‘Allah loves so-and-so, therefore you should love him also,’ and so all the inhabitants of the Heaven would love him, and then he is granted the pleasure of the people on the earth.”