Not by Paul's hand but this may help.
WCF 21:4 Prayer is to be made for things lawful; and for all sorts of men living, or that shall live hereafter: but not for the dead, nor for those of whom it may be known that they have sinned the sin unto death.
The scripture proofs for "but not for the dead" are as follows...
2Sam 12:21 Then said his servants unto him, What thing is this that thou hast done? thou didst fast and weep for the child, while it was alive; but when the child was dead, thou didst rise and eat bread. 22 And he said, While the child was yet alive, I fasted and wept: for I said, Who can tell whether God will be gracious to me, that the child may live? 23 But now he is dead, wherefore should I fast? can I bring him back again? I shall go to him, but he shall not return to me.
Luke 16:25 But Abraham said, Son, remember that thou in thy lifetime receivedst thy good things, and likewise Lazarus evil things: but now he is comforted, and thou art tormented. 26 And beside all this, between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence.
Rev 14:13 And I heard a voice from heaven saying unto me, Write, Blessed are the dead which die in the Lord from henceforth: Yea, saith the Spirit, that they may rest from their labours; and their works do follow them.