Narrated Jabir [radiyallaahu-anhu] that Allaah’s Messenger [sallal-laahu-alayhi-wasallam] said: Iblis places his throne upon water; he then sends detachments [for creating dissension]; the nearer to him in rank are those who are most notorious in creating dissension. One of them comes and says: I did so and so. And he says: You have done nothing. Then one amongst them comes and says: I did not spare so and so until I sowed the seed of discord between a husband and a wife. The Satan goes near him and says: ‘You have done well. A’mash said: He then embraces him. [Saheeh Muslim. Number:2813]
And because of the fact that this bond [between husband and wife] is from the most beloved affairs to Allaah and His Messenger, it is from the most hated affairs to the enemy of Allaah [i.e. shaytaan]. Therefore he hastens to split two people who love another for the sake of Allaah.
[Source: Rawdatul Muhibbeen Wa Nuzhatul Mush-taaqeen. Page:188]