There are times in our daily activities where we encounter a person or situation that incites within us bad or evil thoughts.
These thoughts could be temptations against purity, or they could be thoughts that are directed at a particular person, desiring their harm.
Whatever category these thoughts may be in, God desires that we have good and positive thoughts that bring peace into our hearts.
Here is a prayer from the St. Andrew Daily Missal that helps combats those bad thoughts.