What is the reward for initiating and returning the greeting of peace (Salam), what is the ruling on initiating the greeting of peace to someone you see frequently, and upon entering the mosque, and is it obligatory to return the greeting during prayer?

The Prophet (peace be upon him) explained the reward for initiating and returning a greeting of peace. Whoever says "Assalamu alaikum" (peace be upon you) receives ten good deeds. Whoever adds "wa rahmatullah" (and the mercy of Allah) receives twenty. And whoever adds "wa barakatuh" (and His blessings) receives thirty.

Adding more than "wa barakatuh" is a matter of scholarly disagreement, but the preponderant view is its permissibility. Among the evidences for this are: - The actions of Ibn Umar and Zayd ibn Thabit (may Allah be pleased with them both). - The verse: "So greet with one better than it" [Quran 4:86]. - Weak hadiths that collectively strengthen each other.

The Sunnah is for the rider to greet the walker, the walker to greet the sitter, the few to greet the many, and the young to greet the old. However, if the reverse occurs, it is still sufficient and the reward is attained.

It is Sunnah for one who parts from his brother and then meets him again to greet him with peace, even if this recurs within the same hour.

There is no harm in initiating the greeting of peace upon entering the mosque to those who are seated. A person praying should return the greeting by gesturing, not by speaking. If he responds verbally, his prayer becomes invalid.