The Shaykh’s explanation of the ruling on returning the greeting to a group

The Shaykh : If a Muslim offers the greeting to a group of Muslims and one of them returns it, the obligation falls off the rest. It is not obligatory for every individual in that group to whom the Muslim greeted to return the greeting individually. There is no doubt that it is better for each of them to return it if they wish for good, because the Muslim’s saying “As-salamu alaykum” is, as stated in the authentic hadith, ten good deeds recorded for him. If he says “As-salamu alaykum wa rahmatullah,” it is twenty. If he adds “wa barakatuh,” it is thirty. So if you return the greeting, even if the Muslim greeted a group and you were one of them, you have gained these good deeds. However, the issue is whether it is obligatory for every individual in the group to return the greeting of the one who greeted. The answer is that it is not obligatory; rather, it is obligatory for one of them. It is a collective obligation (fard kifayah). If some of them fulfill it, it falls off the rest. But it is better for the rest to return the greeting, all of them together.
This differs from responding to a sneeze, for it is obligatory for everyone who hears a Muslim sneeze and follow it with praise of Allah the Mighty and Majestic to respond to him, as will be discussed in some of the phrases in the hadith, which explicitly mention responding to the sneeze. Then, regarding offering the greeting, some scholars restrict it, saying, for example, one does not greet the one praying, one does not greet the one reciting, one does not greet the one eating, drinking, or one who is eating and drinking, and the like. Although these statements were made by a group of scholars with their knowledge and virtue, they differed and did not agree, so we have a wide scope to choose from what they differed on what is closest to the truth and correctness.