Shaykh Muhammad Nasiruddin Al-Albani was asked:
Our Shaikh, what is the difference between (عليكم السلام ) and (وعليكم السلام ) ?
“There is no difference and both are allowed. However, perhaps what is better is [to add] the waw (و)”
[Silsilatul-Huda wan-Nur no. 164]
Faisal bin Abdul Qaadir bin Hassan