Guru Gobind Singh Ji reciting Brahm Kavach - Gurbilas P10
The 9th Chapter of Gurbilas Patshahi Dasvi (1797) by Sukha Singh mentions how Guru Gobind Singh was reciting Brahm Kavach and Chandi Chritar while performing a Havan to make the Goddess appear at Nainadevi prior to the creation of the Khalsa.
ਬ੍ਰਹਮੰ ਸੁ ਕਵਚ ਆਦਿੰ ਜੁ ਪਾਠ । ਦਿਨ ਰੈਣ ਠਾਂਢਿ ਠਾਟੰਤ ਠਾਣ । ਸਤਸੈ ਕਥਾਂਨ ਕਥਤੇ ਨਿਧਾਨ । ਜੋ ਗਿਨੈ ਸੁਧ ਬੇਦਾਨ ਜਾਨ ।20।
Brahm Kavach and other similar Banis would be recited day and night while standing with music, the 700 Saloks of the Markhandey Puran [which is the Chritar Chritar] was expounded on by the Treasure Trove [Guru Gobind Singh], which has also been carefully explained and understood in the Vedas.
ਜਿਹ ਭੁਜਾ ਆਠ ਰਾਜਤ ਅਨੂਪ । ਖਗੁ ਸੈਫ ਸਾਂਗ ਧਨੁ ਥਿਰੁ ਸਰੂਪ । [It describes ] The Goddess, who is beautifully adorned with eight arms, whose form resides in the Khag [double edged sword], Saif [straight sword], Saang [metal Spear] and the Dhanu [Bow].
Gurbilas Patshahi 10 (1797), author: Sukha Singh
ਗੁਰਬਿਲਾਸ ਪਾਤਿਸਾਹੀ (੧੭੯੭), ਕ੍ਰਿਤ: ਸੁਖਾ ਸਿੰਘ