Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.

 

In the Name of Allah, the All-Merciful, the Mercy-Giving.

 

All praise is due to Allah. Peace and blessings be upon His Messenger.

 

Almighty Allah says in the Qur’an what means,

 

“And whenever you are greeted with a salutation, then return the greeting with an even better salutation. Or, [at the least,] return it.” (An-Nisaa’ 4:86)

 

According to this Quranic injunction, returning salam greeting is obligatory. To fulfill this obligation, one has to raise his voice enough to let the greeter hear his repaid salam.

 

However, if salam greeting is given for a crowd or a group of persons, returning it becomes a collective, not a personal, duty; that is, if anyone returns it, this is enough to fulfill the obligation.

 

Of course, if one cannot let the greeter hear his/her the repaid salam, due to loud noise, for example, he/she is not sinful.

 

As a general rule, one’s inability to fulfill an obligation, exonerates him/her from liability.

 

Almighty Allah knows best.