Matthew 26:39 - And he went a little farther, and fell on his face, and prayed, saying, O my Father, if it be possible, let this cup pass from me: nevertheless not as I will, but as thou wilt.
Those who hold to Penal Substitution claim that this is a reference to the Father’s penal wrath. The claim is that God’s penal wrath was poured out on Christ as the sins of the world were laid on Christ. But this can’t be true. For Christ told two people that they would drink from this exact same cup:
Matthew 20:23 - So He said to them, “You will indeed drink My cup, and be baptized with the baptism that I am baptized with; but to sit on My right hand and on My left is not Mine to give, but it is for those for whom it is prepared by My Father.”
Now, to punish these people’s sins on Christ and then punish them again on these people is a double payment for these sins. It’s unjust. Therefore, the cup that Christ drank from wasn’t the cup of God’s penal wrath.