Telling the imaam to wait
Question

                I hear some people, when they enter the mosque and the imaam is bowing in rukoo’, telling him that Allaah is with those who are patient, so that the imaam will make the rukoo’ longer and they will be able to join in the rukoo’. Is this permissible?
Praise be to Allah.
    There is no basis for this; it was not done at the time of 
    the Sahaabah (may Allaah be pleased with them) and it is not something that 
    they taught. It also disturbs the others who are praying with the imaam, and 
    disturbing other worshippers is something that is not allowed, because it 
    distracts them. 

    The Prophet  (peace and blessings of Allaah be upon him) 
    went out one night to his companions when they were praying and raising 
    their voices in recitation. He told them not to do that and said: “Do not 
    raise your voices above one another when reciting Qur’aan.” (Maalik in 
    al-Muwatta’, al-Salaah, 29). According to another hadeeth: “Do 
    not disturb one another and do not raise your voices above one another when 
    reciting Qur’aan.” (Abu Dawood, al-Salaah, 1332). This indicates that 
    everything that disturbs the people who are praying behind the imaam is 
    forbidden, because it disturbs the worshippers and interferes with their 
    prayer.

     With regard to the imaam, the fuqaha’ (may Allaah have mercy 
    on them) said: if the imaam senses that someone has come in to join the 
    prayer, then he should wait for him, especially in the last rak’ah in which 
    the latecomer may catch up with the jamaa’ah, because the Prophet  
    (peace and blessings of Allaah be upon him) said: “Whoever catches up with a 
    rak’ah of the prayer has caught up with the prayer.” (al-Bukhaari, 
    al-Mawaaqeet, 580; Muslim, al-Masaajid, 607). But if it will 
    cause any hardship for the members of the congregation then he should not 
    wait, because they are more deserving of consideration than the one who has 
    just come in, because they were there before him.