كتاب صفة القيامة والجنة والنار
52  
Characteristics of the Day of Judgment, Paradise, and Hell
(16)
Chapter: The Mischief Of The Shaitan And How He Sends His Troops To Tempt People, And With Every Person There Is A Qarin (Companion From Among The Jinn)
(16)
بَاب تَحْرِيشِ الشَّيْطَانِ وَبَعْثِهِ سَرَايَاهُ لِفِتْنَةِ النَّاسِ وَأَنَّ مَعَ كُلِّ إِنْسَانٍ قَرِينًا
Sahih Muslim 2813 c

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.
حَدَّثَنِي سَلَمَةُ بْنُ شَبِيبٍ، حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ، حَدَّثَنَا مَعْقِلٌ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، أَنَّهُ سَمِعَ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏ "‏ يَبْعَثُ الشَّيْطَانُ سَرَايَاهُ فَيَفْتِنُونَ النَّاسَ فَأَعْظَمُهُمْ عِنْدَهُ مَنْزِلَةً أَعْظَمُهُمْ فِتْنَةً ‏"‏ ‏.‏
Reference : Sahih Muslim 2813c
In-book reference : Book 52, Hadith 61
USC-MSA web (English) reference : Book 39, Hadith 6756
  (deprecated numbering scheme)