After the last supper
Matt. 26:30 And when they had sung a hymn, they went out to the Mount of Olives.
The hymns they sang that night would have been Psalms 113-118 and a cursory reading of those Psalms points to many of the events of the next 24 hours in the life of Jesus after they left the meal in the upper room.
Psalm 116
3 The snares of death encompassed me;
the pangs of Sheol laid hold on me;
8 For you have delivered my soul from death...
10 I believed, even when I spoke:
“I am greatly afflicted”
Psalm 118
17 I shall not die, but I shall live,
and recount the deeds of the LORD.
and recount the deeds of the LORD.
22 The stone that the builders rejected
has become the cornerstone.
Jesus and his disciples sharing the Passover meal in which pointed to the sacrifice Jesus would soon offer. Then he sings the words describing the cup of salvation that he would soon offer up. As the events unfold that night I don't know how the disciples could forget those words they sang describing the exact events of which they were watching unfold. And we get the comforting truth that Jesus-
"believed, even when I (Jesus) spoke."
My soul is very sorrowful, even to the point of death. Matt. 26:38
Jesus knowing the Psalms knew the Lord would rescue him, that he would not die but he would return to dwell in the house of the Lord forever! (Ps. 23)
Psalms 113-118 are a poetic prophetic description of that night that Jesus was betrayed and even offer insight into what Jesus was thinking and feeling. The cup of salvation that he offers up in his own life is that much more beautiful and glorious understanding these hymns they sang that night.