Imaam Fudayl Ibn Iyaad (rahimahullaah) made du’aa for his son saying:
”O Allaah! I have made strenuous efforts to nurture my son upon (goodness and piety), but I have not been able to nurture him, so nurture him for me.”
Allaah answered Fudayl’s supplication because his son changed and became one of the most righteous people during his era.
[See Siyar A’laam Nubulaa 8/390]