What are the situations in which greeting (giving Salām) is prohibited in Islamic Law, especially the situation related to gatherings of knowledge?

Initiating the greeting of peace (Salaam) is a religious requirement and is considered among the best of Islamic practices. However, scholars have made exceptions to the general command of greeting, identifying situations where it is disliked to initiate it. These include: greeting someone who is occupied with the Adhan (definition) (call to prayer) or Iqama (second call to prayer), reciting the Quran, teaching or listening to knowledge, performing ablution (Wudu'), inside a حمام (bathhouse), eating, or relieving oneself. It has been narrated that the Prophet, peace and blessings be upon him, did not return the greeting to a man who greeted him while he was urinating, which indicates the disliking of returning the greeting in such a situation.