This is one of my favorite dua’as, there are many of course. It’s taken from the Quran (Surah Al Qasas, Ayah 24)
“My Lord, indeed I am, for whatever good You would send down to me in need.”
I just love love love this one! It has the utmost humbleness of a servant asking His Lord for something that He thinks is best! It is said that in time of need if you recite this dua’a endlessly, your needs will be fulfilled in the best manner, inshaAllah!