I couldn’t find a specific, widely known academic text titled Kitab Nuzhatul Muttaqin in my training data. It’s likely that the title is a slight variation or a less common edition of a classical Islamic work. The most probable match is:

– a famous commentary on Riyadh al-Salihin (The Gardens of the Righteous) by Imam al-Nawawi. This commentary is widely used in many Islamic seminaries (especially in South and Southeast Asia) and is often printed in multiple volumes.