Sahih Muslim
The Book Giving Description of the Day of Judgement, Paradise and Hell (Kitab Sifat Al-Qiyamah wal Janna wan-Nar)
Book Number: 039 / Hadith Number: 6756
Jabir reported that Allah's Apostle (may peace be upqn him) said: The Satan sends detachments of his own in order to put people to trial and the highest in rank, in his eyes, is one who is most notorious in sowing the seed of dissension.