Here is the list of activities that results into a decrease in Faith.
1. Ignorance of the names and attributes of Allaah makes a decrease in faith inevitable, because if a man is lacking in knowledge of the names and attributes of Allaah, he will be lacking in faith.
2. Neglecting to think about the signs of Allaah in the universe and the signs of sharee’ah (i.e., verses of the Qur’aan and miracles of the Prophet (peace and blessings of Allaah be upon him), etc.). This causes a decrease in faith or at the very least it causes it to stagnate and not grow.
3. Committing sins, because sin has a profound effect on the heart and on faith. Hence the Prophet (peace and blessings of Allaah be upon him) said: “The adulterer at the time when he is committing adultery is not a believer.”
4. Neglecting to do acts of worship, because neglecting to do acts of worship causes a decrease in faith. But if the act of worship is obligatory and a person neglects it with no excuse, then he is to be blamed and deserves punishment. If the act of worship is not obligatory, or it is obligatory but a person does not do it for a valid reason, then he is lacking but is not to be blamed. Hence the Prophet (peace and blessings of Allaah be upon him) described women as lacking in reason and in religion, and he explained their lacking in religion as being because of the fact that when they menstruate, they do not pray or fast. But they are not to be blamed for not praying or fasting during their menstruation; rather they are commanded not to do these things at that time. But because they miss out on doing some of the things that men do, they are regarded as lacking in this regard.
Source: islamqa.info
