Why do we not join our prayers together?
Question

                I'd like to know why we pray our midday and night prayers all seperately. We know that the prophet used to pray both separetely as well as together. On the day of Arafa we offer our prayers one after the other. In the Qur'an we are told about the prayers thrice daily, morning, modday and night. Why still do we offer our prayers speperately and not one afetr the other.
Praise be to Allah.You have to realize 
          that the question you have asked is very dangerous, because it could 
          be applied to all the rulings of sharee’ah. A person could ask, we do 
          we have to fast a whole month all at once (Ramadaan), why aren’t the 
          days spread out throughout the year? Why is Hajj with its rituals done 
          only at one particular time of the year, when people have to be all 
          crowded together; why can’t it be done at other times of the year too? 
          There are many questions which may imply that one is objecting to the 
          rulings of Allaah. Do you know that Allaah says (interpretation of the 
          meaning): 
“Verily, 
          As Salaah (the prayer) is enjoined on the believers at fixed hours” 
          [al-Nisaa’ 4:103]? 
i.e., it is obligatory at those times. So understand what has been 
          said above, and I ask Allaah to guide you and set your heart straight. 
           
Shaykh Sa’d al-Humayd  
Islam means submitting to Allaah and not 
          objecting to His commands. Allaah says (interpretation of the meaning): 
          
“It 
          is not for a believer, man or woman, when Allaah and His Messenger have 
          decreed a matter that they should have any option in their decision” 
          [al-Ahzaab 33:36]  
And Allaah says concerning the timings 
          of the prayer: 
“Verily, 
          As Salaah (the prayer) is enjoined on the believers at fixed hours” 
          [al-Nisaa’ 4:103]  
The wahy (revelation, i.e., Qur’aan and 
          Sunnah) described the times of prayer in both word and deed. This is 
          how the Prophet  (peace and blessings 
          of Allaah be upon him) did the prayers during his lifetime; he did not 
          join prayers together except when he was travelling or at times of hardship. 
          
 We also want to advise you that there 
          are some followers of bid’ah (reprehensible innovation) who say that 
          Zuhr and ‘Asr should be joined together, as should Maghrib and ‘Ishaa’, 
          even when one is not travelling and for no reason. Beware of these people, 
          do not keep company with them and do not listen to them. Beware of them 
          lest they lead you astray from your religion. We ask Allaah to grant 
          you strength and guidance.