Ref. No. 934
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
The Sunnah of the Prophet Muhammad (saws) of two types; Sunnat-e Muakkadah (which the Prophet did persistently) and Sunnat-e Ghair-Muakkadah (which the prophet did but did not do persistently).
Sunnat-e Muakkadah brings a great deal of reward. Hence, it is a sin to abandon the sunnat e muakkadah for no reason. While leaving the sunnat e Ghair muakkadah is not a sin. But the one who neglects this suunah is missing out on a great reward. Acting upon sunnat Ghair Muakkadah is also a virtuous deed, one should follow it too. For detail you had better study the book “Talimul Islam”.
And Allah knows best
Darul Uloom Waqf Deoband