The Fatima Prayer is a brief prayer to Jesus, traditionally said after each decade of the Rosary. It originated from the reported apparitions of Our Lady of Fatima in Portugal in 1917.
O My Jesus, forgive us our sins, save us from the fires of Hell and lead all souls to Heaven, especially those who are in most need of Thy mercy.
The original prayer was in Portuguese and never had a Latin version so the one given is a reconstruction in the style of liturgical Latin prayers.
Dómine Jesu, dimitte nobis débita nostra, salva nos ab igne inferni, perduc in caelum omnes ánimas, praesertim eas, quae misericórdiae tuae máxime indigent.
Ó meu Jesus, perdoai-nos e livrai-nos do fogo do inferno; levai as almas todas para o Céu, principalmente aquelas que mais precisarem.
For Catholics who accept the Fatima apparitions as worthy of belief, the prayer is understood to have been given through a private revelation. The Catholic Church has approved devotion connected with Fatima, but Catholics are not required to believe in private revelations, even approved ones.
I'm not sure how I feel about the, "You're allowed to optionally believe this," part of Catholic life. When it's put into my hands to decide what's real or not, I'm honestly not sure. I prefer when I can just put my faith into Catholicism and simply benefit from that obedience.
But I suppose it's sometimes prudent for the Church to avoid binding consciences beyond what the faith itself requires.
Nevertheless it's a good prayer.