I was told this sakhi by a very gurmukh singh. Once Bhai Sahib Randhir Singh jee visited a Nihang Chaunni in Sri Anandpur Sahib. It was early morning and Bhai Sahib saw a Nihang Singh sitting cross-legged in his tent and doing Vaheguru Vaheguru.... He was in complete anand with his eyes and head raised upwards.
Bhai Sahib on seeing this told his fellow singh that this Nihang is a Dasam Duaari. In his previous life, he was a Nihang Singh and did immense langar de seva. He used to prepare langar day and night. Even in scorching summer heat, he used to do langar de seva. As a result of his Langar Seva, Dashmesh Pita blessed him with Dasam Duar in this life.