Al-A’mash reported: Ibrahim al-Nakha’i, may Allah have mercy on him, said, “If you greet a single person with peace, then say: Peace be upon you all. Verily, the angels are with him.”
Source: Tafsīr al-Qurṭubī 4:86
عن الْأَعْمَش عن عَنْ إِبْرَاهِيمَ النَّخَعِيِّ رحمه الله قَالَ إِذَا سَلَّمْتَ عَلَى الْوَاحِدِ فَقُلِ السَّلَامُ عَلَيْكُمْ فَإِنَّ مَعَهُ الْمَلَائِكَةَ
4:86 تفسير القرطبي