Shaykh Abdul-Muhsin Al-Abbaad was asked:
How does a person know, if he prays Istikhaarah, that Allah chose this affair for him and is pleased with him doing it?
“If his soul inclines towards it, then he gives precedence/preferrence to it. This is the legislated path. That is: when a person makes istikhaarah, if his soul inclines to an action, he performs it. If his soul inclines to leave it, he leaves it. This is what a person is capable of doing. And Tawfeeq (success) is in the Hand of Allah, the Exalted”
[Sharh Sunan Nasaai no. 139]
Faisal Ibn Abdul Qaadir Ibn Hassan