When you have a bad suspicion ...

When you have a bad suspicion about a Muslim in your heart, you should increase your consideration toward him and make dua for him. This way you will infuriate Satan and will be able to drive him away. Because of this, Satan will be reluctant to put evil thoughts into your heart, afraid that you would increase your consideration towards your brother and will make dua for him again.
 Al-Ghazali

Quotes from the same author

It is sometimes said that we drink our religion with our mother's milk.
 Al-Ghazali
To completely trust in Allah is to be like a child who knows deeply that even if he does not call for the mother, the mother is totally aware of his condition and is looking after him.
 Al-Ghazali
Neglect not your time, nor use it haphazardly; on the contrary you should bring yourself to account. Structure your litanies and other practices during each day and night. This is how to bring about the spiritual blessing (baraka) in each period. If each of your breaths is a priceless jewel, Be not like the deceived fools who are joyous because each day their wealth increases while their life grows ever shorter.
 Al-Ghazali
Knowledge without action is wastefulness and action without knowledge is foolishness.
 Al-Ghazali
Man's nature is made up of four elements, which produce in him four attributes, namely, the beastly, the brutal, the satanic, and the divine. In man there is something of the pig, the dog, the devil, and the saint.
 Al-Ghazali