The whole point about rehit-namas and the differences between them is a whole discussion in itself, but there is evidence in Bhangu's Panth Prakash, Sainapati's Gursobha, Prem Sumarag Granth.
There is also notice of this in the earliest european sources from the late 1700s.
No one is telling anyone to do these things, but to whitewash your own people's history is weak.
As alluded to previously, the people who did partake aren't likely to have done so for what we call 'recreational reasons' today. It may as well have been medical reasons? Given how sukha da tehl is being increasingly investigated by modern science along this very line, it isn't implausible. It may well have been a carry over from pre-existing Ayurvedic practice?
Can't you people have a grown up discussion about this?
100 or so years from now, historical observations from the late 80’s and early 90’s armed resistance of Khalistan Guerrilla Fighters is going to be examined and debated upon. They will find some of the Guerrilla fighters used Afeem (Opium) to help them stay alert and fight fatigue during the harsh times when they were being hunted or carrying out missions. Examining this through the present we can say that by no means was ‘Afeem’ a part of their Rehit Marayada, or were they encouraged or given exemption by the Jathedar of Akal Takhat to do so. They did this because they simply chose to do so.
Unless anyone can submit evidence from Sikh sources or written Hukamnama from the 18th Century that taking Bhang was part of Sikh Rehit Marayada, this is no more than an observation of ‘some Sikhs who chose to do so’.
Maybe our ancestors had an inkling of the health and psychological benefits of certain components of sukha? Look at these goray, they are now selling sukha da telh with haldhee mixed in.