He then lying on Jesus' breast saith unto him, Lord, who is it?

People's New Testament

13:24,25 Simon Peter there beckoned to him. The disciples did not know who would be the traitor. At Peter's request, John, in a low tone, asked Jesus.

Wesley's Notes

13:25 Leaning down, and so asking him privately.

Jamieson-Fausset-Brown Bible Commentary

25. He then lying-rather leaning over on Jesus' bosom.

saith-in a whisper, "Lord, who is it?"

Matthew Henry's Concise Commentary

13:18-30 Our Lord had often spoken of his own sufferings and death, without such trouble of spirit as he now discovered when he spake of Judas. The sins of Christians are the grief of Christ. We are not to confine our attention to Judas. The prophecy of his treachery may apply to all who partake of God's mercies, and meet them with ingratitude. See the infidel, who only looks at the Scriptures with a desire to do away their authority and destroy their influence; the hypocrite, who professes to believe the Scriptures, but will not govern himself by them; and the apostate, who turns aside from Christ for a thing of naught. Thus mankind, supported by God's providence, after eating bread with Him, lift up the heel against Him! Judas went out as one weary of Jesus and his apostles. Those whose deeds are evil, love darkness rather than light.