Missing this prayer is not considered to be a sin. Nafl: The last of the four main types of prayer, Nafl is not compulsory and is usually performed for an extra virtue.
However, missing the latter one, which is said to be practiced intermittently by Prophet Muhammad (PBUH), is not considered punishable. The former is to be practiced regularly, and missing the same is regarded as a sin.
Prayer (Salat) - one of the Five Pillars of Islam, is segregated into four main types: It is a night prayer that is offered to attain mental strength and peace. Tahajjud prayer is a nafl or voluntary prayer.
