When is the phrase "in sha' Allah" (God willing) said, and is it used to conclude supplications?

The phrase "In sha' Allah" (God willing) is said when resolving to do something in the future or expecting something to happen, and it contains great reverence towards God. Allah warned the Prophet, peace be upon him, to adhere to it, as in the story of Sulaiman (Solomon), peace be upon him, who did not say it and thus missed his need. As for ending a supplication with it, that is not appropriate, as it is disliked to make a supplication conditional on God's will; what is required from the supplicant is determination and persistence.