Ruling on standing up to welcome a newcomer
Question

                A man came in when I was in a gathering, and the people present stood up for him, but I did not stand up. Do I have to stand up? Is there any sin on those who did stand up?
Praise be to Allah.You 
          do not have to stand up for someone who comes in, but it is good manners, 
          if someone stands up for you, to shake his hand, especially the head 
          of the household and prominent people. This is the matter of good manners. 
          The Prophet 
          
          (peace and blessings of Allaah be upon him) stood up for Faatimah, and 
          she stood up for him, may Allaah be pleased with her. The Sahaabah (may 
          Allaah be pleased with them) stood up, on the Prophet’s command, for 
          Sa’d ibn Mu’aadh when he came to pass judgement on Bani Qurayzah. Talhah 
          ibn ‘Ubayd Allaah (may Allaah be pleased with him) stood up in front 
          of the Prophet 
          
          (peace and blessings of Allaah be upon him) when Ka’b ibn Maalik (may 
          Allaah be pleased with him) came after Allaah had accepted his repentance; 
          he shook his hand and congratulated him, then sat down. This is the 
          matter of good manners and this is broad issue. What is denouncable 
          is when people stand up and remain standing by way of veneration. But 
          if a person stands up to welcome his guest and honour him, or to shake 
          hands with him or greet him, this is something which is prescribed in 
          Islam. But to remain standing when people are sitting by way of veneration, 
          or standing at the door without greeting anyone or shaking hands with 
          anyone, this should not be done. Even worse than that is standing up 
          to venerate a person when he is sitting down, not for the sake of guarding 
          him but only for the purpose of veneration.
There 
          are three kinds of standing up, as the scholars said :
  
          

        (1)          
          When people stand up for someone to venerate 
          him when he is sitting down, as the Persians venerated their kings and 
          leaders, as described by the Prophet 
          
          (peace and blessings of Allaah be upon him). This is not permitted, 
          and for this reason the Prophet 
          
          (peace and blessings of Allaah be upon him) told them to sit down when 
          he led them in prayer sitting down. He told them to sit down and to 
          pray behind him seated, and when they stood up he said, “You almost 
          venerated me like the Persians venerate their leaders.” 

        (2)
         
          When a person stands up when another person comes 
          in or goes out, without greeting him or shaking hands with him, rather 
          simply in order to venerate him. This at the very least is makrooh. 
          The Sahaabah (may Allaah be pleased with them) used not to stand up 
          for the Prophet 
          
          (peace and blessings of Allaah be upon him) when he came in to them, 
          because they knew that he 
          
          (peace and blessings of Allaah be upon him) disliked that. 

(3)
         
When a person stands up for someone who has come 
in, in order to shake his hand or to take his hand and lead him to a 
          seat, etc. There is nothing wrong with that, rather it is the Sunnah 
          as mentioned above.