Are the scholarly differences concerning one who does not pray and ruling by
laws other than those revealed by Allaah to be taken into account?
Question

                I was told in the time of the Salaaf they would differ on issues such as the one who did not perform prayer and the on the one who ruled by laws other than what Allah has revealed, is it true this is called Khilaf Al Mu`tabar (A difference which is taken into consideration)?.
If the Salaaf did differ may I please ask whom of the Salaaf differed on both of these issues?
May Allaah increase you my beloved shaykh in good and give you the ultimate reward, heaven with the messenger of Allah (Sal`Allahu Alaihi Wa Sallam).
Praise be to Allah.There are differences between the Islamic madhhabs
      whose views may be taken into consideration concerning the ruling on one
      who does not pray. The dispute is only with regard to the one who does not
      deny that the prayer is obligatory. The person who denies that prayer is
      obligatory is definitely a kaafir. The majority of the Salaf, of the
      Sahaabah and Taabi’een, were of the view that the person who does not
      pray is a kaafir, because of the saheeh texts which clearly state that.
      The dispute arose after their time, but the scholars who examined this
      issue said that the opinion stated is the more sound view, that the person
      who does not pray is guilty of major kufr which puts him beyond the pale
      of Islam. This is the opinion according to which fatwas are issued
      nowadays.
      
      
      With regard to ruling according to laws other than those revealed by
      Allaah, whilst acknowledging that the ruling of Allaah is more complete
      and more perfect, and more beneficial to mankind than any other (law), a
      group of scholars said that this is a lesser form of kufr. But giving
      preference to man-made laws and giving them precedence over the laws
      (sharee’ah) of Allaah, and believing that the laws of Allaah are not
      suitable for our times, for example, this is a form of major kufr which
      puts a person beyond the pale of Islam. The dispute among the scholars in
      this case has to do with the person who judges according to laws other
      than those revealed by Allaah, whilst still believing that the laws of
      Allaah are more perfect and more fitting – is he guilty of major kufr or
      a lesser form of kufr? Because Allaah has described those who rule
      according to laws other than His in different ways, sometimes as kaafirs,
      sometimes as faasiqoon (evildoers), sometimes as zaalimoon (wrongdoers).
      This is to be interpreted either as referring to different cases in which
      people rule according to laws other than those revealed by Allaah, or as
      meaning one and the same thing, because the kaafir is also a faasiq and a
      zaalim.