This book is a translation of Ibn Rajab's treatise Al-Mahajjah fi Sayri'l-Dulja which is an explanation of the following hadeeth of the Prophet (ﷺ):
Narrated Abu Huraira:
Allah's Messenger (ﷺ) said, "The deeds of anyone of you will not save you (from the (Hell) Fire)." They said, "Even you (will not be saved by your deeds), O Allah's Messenger (ﷺ)?" He said, "No, even I (will not be saved) unless and until Allah bestows His Mercy on me. Therefore, do good deeds properly, sincerely and moderately, and worship Allah in the forenoon and in the afternoon and during a part of the night, and always adopt a middle, moderate, regular course whereby you will reach your target (Paradise).
Sahih al-Bukhari: 6463.