This salutation phrase appears seven times in the Quran, each time Salamun ʿalaykum ( سَلَامٌ عَلَيْكُمْ). However, Classical Arabic, used in the Qur'an and early Hadith manuscripts, the phrase is spelled as ٱلسَّلَٰمُ عَلَيْكُمْ وَرَحْمَتُ ٱللَّٰهِ وَبَرَكَٰتُهُ. In Rasm, it is written as السلم علىکم ورحمٮ الله وٮرکٮه.
Surah Al-An'am (6), Ayah 54:
وَإِذَا جَآءَكَ ٱلَّذِينَ يُؤْمِنُونَ بِآيَاتِنَا فَقُلْ سَلَامٌ عَلَيْكُمْ ۖ كَتَبَ رَبُّكُمْ عَلَىٰ نَفْسِهِ ٱلرَّحْمَةَ ۖ أَنَّهُۥ مَنْ عَمِلَ مِنكُمْ سُوٓءًۢا بِجَهَالَةٍۢ ثُمَّ تَابَ مِنۢ بَعْدِهِۦ وَأَصْلَحَ فَأَنَّهُۥ غَفُورٌۭ رَّحِيمٌۭ
"When those who have faith in Our signs come to you, say, 'Peace to you! Your Lord has made mercy incumbent upon Himself: whoever of you commits an evil [deed] out of ignorance and then repents after that and reforms, then He is indeed All-Forgiving, All-Merciful.'"
The Prophet (ﷺ) said, "Allah created Adam, making him 60 cubits tall. When He created him, He said to him, "Go and greet that group of angels, and listen to their reply, for it will be your greeting (salutation) and the greeting (salutations of your offspring." So, Adam said (to the angels), As-Salamu Alaikum (i.e. Peace be upon you). The angels said, "As-salamu Alaika wa Rahmatu-l-lahi" (i.e. Peace and Allah's Mercy be upon you). Thus the angels added to Adam's salutation the expression, 'Wa Rahmatu-l-lahi,' Any person who will enter Paradise will resemble Adam (in appearance and figure). People have been decreasing in stature since Adam's creation.
May Allāh (سبحانه و تعالى) help us understand Qur'ān and follow the Sunnah of Prophet Muhammad ﷺ, which is embodiment of commandments of Allah contained in the Qur'ān. May Allah help us to be like the ones He loves and let our lives be lived helping others and not making others' lives miserable or unlivable. May all our wrong doings, whether intentional or unintentional, be forgiven before the angel of death knocks on our door.