GURMAT SUDHĀKAR (lit. Sikh principles explained and illustrated : Sudhākar= the moon, i.e. the illuminator) is an anthology by Bhāī Kāhn Siṅgh, of Nābhā, of excerpts from old Sikh historical texts and manuals of stipulated conduct. The work, first published in 1899, is divided into sixteen chapters. The opening chapter comprises verses from Gurū Gobind Siṅgh, the second from Bhāī Gurdās and the third passages from the Janam Sākhī of Bhāī Bālā. The fourth chapter is culled from Gurbilās Chhevīṅ Pātshāhī. Chapter five is based on Vār 1 from Bhāī Gurdās. Chapter six repeats the commentary on Vār XI of Bhāī Gurdās. Chapters seven and eight contain the sayings of Bhāī Nand Lāl and of Bhāī Desā Siṅgh. The ninth chapter summarizes the book Prem Sumārag. Chapters ten and eleven present sayings from the Rahitnāmā of Bhāī Chaupā Siṅgh and the sayings of Bhāī Dayā Siṅgh. Chapter twelve contains verses from Srī Gur Sobhā of Saināpati, poet contemporary of Gurū Gobind Siṅgh. Chapter thirteen offers excerpts from the famous historical text, the Panth Prakāsh. Chapters fourteen and fifteen consist of sayings from Gurū Gobind Siṅgh and chapter sixteen reproduces verses from Gurū Nānak Prakāsh and Srī Gur Pratāp Sūraj Granth.
These extracts from old Sikh sources are heavily annotated. Each work is appropriately introduced at the beginning of each chapter.
The book remained out of print for many years until it was reprinted in recent years (1970) by the Languages Department, Punjab.