Shaykh Bin Baz was asked:
If a person is resolved in doing something, does he pray Istikharah or not?
“What is apparent is that Istikharah is [performed] when there is uncertainty whether there is a benefit in something for him [or not]. There is no need for Istikharah if he is certain. It comes in the Hadith:
إِذَا هَمَّ أَحَدُكُمْ بِالأَمْرِ
If anyone of you intends to do something
The intend of the context is doubt. As for if you know that this affair is good for you, then there is no Istikharah. You know prayer is good for you, that fasting is good for you, that being dutiful to your parents is good for you, then there is no need to do Istikharah. Istikharah is only for something that has ambiguity”.
[al-Fawaaid al-‘Ilmiyyah min Duroos al-Baaziyyah (5/56)]
Faisal Ibn Abdul Qaadir Ibn Hassan