Al-Qasas • BN-TAFSEER-IBN-E-KASEER
﴿ ٱلَّذِينَ ءَاتَيْنَٰهُمُ ٱلْكِتَٰبَ مِن قَبْلِهِۦ هُم بِهِۦ يُؤْمِنُونَ ﴾
“As for those unto whom We have vouchsafed revelation aforetime - they [are bound to] believe in this one [as well];”
Please check ayah 28:55 for complete tafsir.