Is continuing to neglect a confirmed Sunnah is sin?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

A Muslim is required to perform as many good deeds as he can, especially those which are confirmed in the Sunnah. The scholars stated that abandoning the Witr prayer and Rawaatib prayers (i.e. confirmed or unconfirmed supererogatory prayers that are performed either before or after the obligatory prayers) is considered as one of the legal defects the lead to the rejection of one's testimony. A person abandoning them is like the one who is turning away from the Sunnah of the Prophet . The Prophet said: "Whoever turns away from my Sunnah is not from me (does not belong to me)." [Al-Bukhaari and Muslim]

The author of Mughni Al Muhtaaj said: "Continuously abandoning Rawaatib Sunan (plural of Sunnah) and desirable actions of the prayer is considered as one of the legal defects the lead to the rejection of one's testimony, because the person who does so is neglecting his religion and not taking care of the serious matters (of Shariah)."

However, the scholars differed in opinion whether or not such a person is sinful. The author of Al-Insaaf said: "It is not permissible to be habituated to abandoning the Rawaatib Sunan." However, the author of Al-Furoo’ said: "There is no sin in abandoning a Sunnah (prayer)."

In conclusion, abandoning confirmed Sunan is a sign of carelessness and lack of concern regarding Islamic matters, although the preponderant opinion is that the person who does so is not sinful.

Allaah Knows best.