Permissibility of offering the optional late night Prayer in the place where one is guarding

Q 2: What is the ruling on performing Salat-ul-Tahajjud (optional late night prayer) while I am on guard duty? It is worth mentioning that I can offer it easily and without problem; am I sinful in this?

A: It is permissible for those who are on guard duty to offer the Nafilah (supererogatory Prayer) at the place they are guarding, if doing so does not affect their obligations to their work of guarding.