Following is the Fatwa of Shaykh Abdul Mannan Noorpuri Rahimullah
If the sunnah prayer is left which is other than obligatory prayers, Is it a sin? If it is a sin then whether it is a small sin or big sin?
The question of obligatory prayers will be asked first in the hereafter, If there would be a mistake in obligatory prayers then the Voluntary prayers will perfect them. And if the person will have no Voluntary prayers then he will fail the exam of obligatory prayers, he will also be a sinner in this case. So leaving the Voluntary and Sunnah prayers is a sin in this regard. But I don`t know whether it is a small sin or Big sin.
How is it that If all the Sunnah prayers before and after the obligatory prayers are left? A Molvi says that do not pray the Sunnah or Voluntary prayers, If Allah will ask then I will answer?
This is a deal of loss. The hadith of Abu Dawud is The question of prayer will be asked first on the Day of Judgment, If it is defective, then optional prayer will perfect it. Now consider this point that If someone has no voluntary prayers other then obligatory prayers then what will he do in the case of defect in the obligatory prayers? The Molvi is taking the responsibility right now but he will not take this responsibility on the day of judgment. So, do not come under his words, then there is something like Thanking God. Prophet peace be upon him said “should I not prove myself to be a thanksgiving servant (of Allah)?” [Quran wa Hadeeth ki Roshni me Ahkam wa Masail 1/216]