Saint Cyprian of Carthage, pray for us!

One of our Early Church Fathers from the first century of Christians talks about praying for the dead and vice-versa.  So, this is a later "invented doctrine"? Apparently not.

"Let us remember one another in concord and unanimity. 

Let us on both sides of death always pray for one another. 

Let us relieve burdens and afflictions by mutual love, that if one of us, by the swiftness of divine condescension, shall go hence the first, our love may continue in the presence of the Lord, and our prayers for our brethren and sisters not cease in the presence of the Father’s mercy."

~~ Saint Cyprian of Carthage (190-158) Martyr, Father of the Church, Memorial Day: September 16

NOTE: The underlining is, of course, my own emphasis!