Ruling on member of the congregation leaving straight after the imam says the salaam

Once the imam has said the
salaam, it is permissible for the person who prayed behind him to move,
whether the imam has turned to face the congregation or has stayed where he
is, or he has got up from his place. But it is better for the person who
prayed behind him to stay put until the imam turns to face the congregation,
because of the possibility that the imam may be sitting so that he can do
the two prostrations of forgetfulness (sujood al-sahw) after saying the
tasleem at the end of the prayer. Even better than this is to get up only
after the imam has got up. 

There is an indication that
it is permissible to leave as soon as the salaam has been said in the report
narrated by al-Bukhaari (875) from Umm Salamah (may Allaah be pleased with
her) who said: When the Messenger of Allaah (peace and blessings of
Allaah be upon him) said the salaam, the women got up when he finished his
tasleem and he stayed in his place for a while before getting up. One of the
narrators of the hadeeth said: We think, and Allaah knows best, that this
was so that the women could disperse before any of the men caught up with
them. 

With regard to the report
narrated by Muslim (426) from Anas (may Allaah be pleased with him) who
said: The Messenger of Allaah (peace and blessings of Allaah be upon
him) led us in prayer one day, and when he had finished praying he turned to
face us and said: “O people, I am your imam, so do not go ahead of me in
bowing, prostrating, standing or finishing, for I can see you from in front
of me and behind me,” what is meant by “finishing” here is the salaam. 

Al-Nawawi (may Allaah have
mercy on him) said: The words of the Prophet (peace and blessings of
Allaah be upon him): “so do not go ahead of me in bowing, prostrating,
standing or finishing” indicate that it is haraam to do these things and
others that are similar to them. What is meant by finishing is the salaam.
End quote. 

Imam al-Shaafa’i (may
Allaah have mercy on him) said in al-Umm (1/151): The one who has
prayed behind an imam may leave when the imam has finished the salaam,
before the imam gets up, and he may delay that and leave after the imam
leaves, or leave with him, which I like better. End quote. 

Ibn Qudaamah (may Allaah
have mercy on him) said in al-Mughni (1/328): It is mustahabb for the
one who has prayed behind an imam not to get up and leave before the imam, in case he remembers something that he forgot and does the prostration of forgetfulness. End quote. 

And Allaah knows best.