That is Jesus, the son of Mary - the word of truth about which they are in dispute.
The Saheeh International Quran Translation
ذَٰلِكَ عِيسَى ٱبْنُ مَرْيَمَ قَوْلَ ٱلْحَقِّ ٱلَّذِى فِيهِ يَمْتَرُونَThat is Jesus, the son of Mary - the word of truth about which they are in dispute.