Q: May we include the Fatima prayer when reciting the rosary?
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A: The prayer was included in the description of the rosary in the USCCB Catholic Household Blessings & Prayers. Here is what it says:
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(After finishing each decade, some say the following prayer requested by the Blessed Virgin Mary at Fatima: “O my Jesus, forgive us our sins, save us from the fires of hell, lead all souls to heaven, especially those who have most need of your mercy.”)
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I read this to mean that it is optional. Those who use it would be advised to pray the version published by the USCCB for the sake of uniformity.