Consider Ayat 21, Surat Ahzab...

[Abu Hafsat]

As-Salaam alaikum, 

"There is for you in the Envoy of Allah an excellent example (uswa)".. /33:31.

This ayat/verse forms the basis of the very first Muslims setting their hearts on finding out about the behavior of the Prophet Muhammad, Sallallahu alaihi Wasallam. They made efforts to find out from him or those close to him, to acquaint themselves with even the minutest details of his tastes, his preferences, and his way of reacting in any given circumstance. 

Deprived of the physical presence of the Messenger of Allah, Sallallahu alaihi Wasallam, the succeeding generations of Muslims down to our time today, did everything possible to conserve the memory of his Sunnah, his custom, by collecting together the hadiths. These are testimonies going as far back as the first generation of Muslims, which rescued  the sayings and actions of the Prophet or of his companions, and they are gathered into a vast corpus of which 6 books are reputed to be canonical. These are :-

(1) Sahih Bukhari of Imam Muhammad Ibn Isma'il Al-Bukhari. 

(2) Sahih Muslim of Muslim ibn al-Hajj. 

(3) Sunan Abu Dawud of Abu Dawud al-Sijjistani

(4) Ibn Majah 

(5) Sunan al-Tirmidhi of Abu Isa al-Tirmidhi and

(6) Al-Nisa'i of Ahmad Ibn Shu'ayb Al-Nisa'i. 

Subjects and issues covered in the above 6 authenticated books of hadith included actual rituals (the Ibaadat) social behavior (the mu'amalat) and everyday actions--eating, drinking sleeping etc. 

This way, the Prophetic Sunnah is preserved for Muslims to observe it today in accordance with the above quoted ayat (33:21) and in compliance with ayat 31 in Surat Al-i-Imran:

"Say, if you love Allah, follow me (ittabi'uni), Allah will love you".. (3:31).

as following the Prophet, Sallallahu alaihi Wasallam, is the only means of access to the highest spiritual realization.