Our Lady taught this prayer to the three shepherd children at Fatima in 1917, asking that it be prayed after each decade of the Rosary for the conversion of sinners and the souls in Purgatory.
English
O my Jesus,
forgive us our sins,
save us from the fires of hell,
and lead all souls to Heaven,
especially those in most need of thy mercy.
Amen.
Portuguese (Original)
O meu Jesus,
perdoai-nos, livrai-nos do fogo do inferno,
levai as almas todas para o Ceu,
principalmente aquelas que mais precisarem.
Origin: Given by Our Lady to Lucia, Francisco, and Jacinta at Fatima, Portugal, on July 13, 1917. The Portuguese word "alminhas" (little souls) tenderly embraces all souls who most need God's mercy.