If the greeting is given to a person who is performing Prayer, how should he respond? Sunan Ibn Majah 1019

Arabic hadith text
حَدَّثَنَا أَحْمَدُ بْنُ سَعِيدٍ الدَّارِمِيُّ، حَدَّثَنَا النَّضْرُ بْنُ شُمَيْلٍ، حَدَّثَنَا يُونُسُ بْنُ أَبِي إِسْحَاقَ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي الأَحْوَصِ، عَنْ عَبْدِ اللَّهِ، قَالَكُنَّا نُسَلِّمُ فِي الصَّلاَةِ فَقِيلَ لَنَا إِنَّ فِي الصَّلاَةِ لَشُغْلاً ‏.‏
Translation
It wasnarrated that ‘Abdullah said

“We would greet others duringtheprayer, and it was said to us: ‘During the prayer one ispreoccupied.’”