Is "Peace be upon you" to be said before turning right in prayer, or concurrently with it? Is the Iqamah obligatory before prayer, and if forgotten, does the prayer become invalid? Is it obligatory to stand upon hearing the Adhan in the mosque?

The salutation (taslim) begins by saying "Assalamu Alaykum" facing the qibla, then the worshiper turns to the right and left, saying "wa Rahmatullah." The iqama (call to commence prayer) is a Sunnah, and it is also said to be Fard Kifaya (a collective obligation). The prayer is not invalidated by omitting it. It is preferable for someone who enters during the adhan (call to prayer) to wait for the muezzin to finish so they can repeat the adhan to gain reward.