A scholar of the past said regarding the difference between customary and shar’i acts:
“You should also know that the capacity which is most specific to God’s Messenger is that of legislation, because that was God’s primary objective in sending him to mankind. Indeed God has stated in the Quran that legislation was the Prophet’s exclusive quality.
“Muhammad is only an apostle” [3: 144].
For this reason we should consider the statements and actions that ensued from God’s apostle relating to the general condition of the Muslim community to be a matter of legislation unless there is circumstantial evidence to the contrary.” (Treatise on Maqasid al-Sharia, p. 50)
Thus the Asl (default) is that everything the Prophet (saw) does is to be followed and is guidance unless there is evidence to suggest otherwise. This means that the burden of proof will be on those who claim a certain action is from the Prophet’s (saw) customary acts (jibiliyya) and not those who claim that it is part of the Shari’ah.