Q: Some people use Salamun alaikum instead of Assalamu alaikum to say salaam. Which is the correct one, and what's the difference?

Answer: Both ways to do Salaam are correct, as both appear in the Holy Quran.

وَإِذا جاءَكَ الَّذينَ يُؤمِنونَ بِآياتِنا فَقُل سَلامٌ عَلَيكُم ۖ كَتَبَ رَبُّكُم عَلىٰ نَفسِهِ الرَّحمَةَ ۖ أَنَّهُ مَن عَمِلَ مِنكُم سوءًا بِجَهالَةٍ ثُمَّ تابَ مِن بَعدِهِ وَأَصلَحَ فَأَنَّهُ غَفورٌ رَحيمٌ

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.’ (6:54)

فَأتِياهُ فَقولا إِنّا رَسولا رَبِّكَ فَأَرسِل مَعَنا بَني إِسرائيلَ وَلا تُعَذِّبهُم ۖ قَد جِئناكَ بِآيَةٍ مِن رَبِّكَ ۖ وَالسَّلامُ عَلىٰ مَنِ اتَّبَعَ الهُدىٰ

So approach him and say, “We are the apostles of your Lord. Let the Children of…