Allah (SWT) says in the noble Qur’an:
and they follow what the Satan’s recited over Sulayman's Kingdom. Sulayman disbelieved not but the Satan’s disbelieved, teaching the people sorcery, and that which was sent down upon Babylon's two angels, Harut and Marut; they taught not any man, without they said, 'We are but a temptation; do not disbelieve ' From them they learned how they might divide a man and his wife, yet they did not hurt any man thereby, save by the leave of Allah, and they learnt what they hurt them and did not profit them, knowing well that whosoever buys it shall have no share in the world to come; evil then was that they sold themselves for; if they had but known. Al-Qur’an, 2:102
Jabir (RA) reported that the prophet (PBUH) said:
Iblis would lay his throne on water and would send his brigade of demons, The lowest among them in rank is the one who is most notorious in stirring up fitna. One of the demons would, after a mission, come and say to Iblis, 'I have done so and so.' iblis would reply, 'You have not done anything.' Another one would come and say: 'I have not left such and such person until I separated him from his wife ' Iblis would come closer to his demon and say, 'How good you are'. Sahih Muslim in An-Nawawi. 17/157
Types of Sihr of Separation
According to Al-Hafiz Ibn Kathir, the cause of separation between two spouses through this sihr is that each of them appears to the other as an ugly or ill-mannered person.
(Tafsir Ibn Kathir: 1/144)