Hakim al-Umma Hadhrat Mawlana Ashraf ‘Ali Thanawi (may Allah have mercy on him) said,
“The quarters of the heart should not be left vacant.
If they are not occupied with Allah’s remembrance(dhikr) fill them with something else that is permissible (mubah).
Otherwise, seeing them vacant Satan will move into them and take hold (of the heart).”
Waaz: Arza al-Haqq, Khutbat e Hakim al-Ummat, volume 15, page95