Answered by Shaykh Faraz Rabbani
Most of the time I pray, I pray only the Fardh and Sunnah Muakkadah and Witr. For instance, in Isha salaat, I only read the 4 Fardh, 2 Sunnat and 3 Witr.I would like to know if this is permissible and am I sinning for leaving my out my 4 sunnat and 4 nafl of Isha?
And also, under what circumstances can one leave out the sunnah ghair- muakkadah and nafl of Zuhr, Asr, Maghrib and Isha? Is it only under extreme circumstances or when one feels like it?

Walaikum assalam,
It is not sinful to leave voluntary prayers (such as nafl or sunna ghayr mu’akkada). However, one does lose some reward.
[See attached answers.]
For details of the confirmed and unconfirmed sunna prayers, see the Prayer section at (http://www.sunnipath.com)
Wassalam,
Faraz Rabbani