Beef was banned by 18th century Khalsa and by Maharaja Ranjit Singh

[shastarSingh]

E. Samuels- Asiatic annual register-1809

Now become a Singh, Ire is heterodox, and distinct from the Hindoos, by whom he is considered as an apostate. He is not restricted in his diet, but is allowed, by tlie tenets of his new religion, to devour whatever food his appetite may prompt, excepting beef.

[shastarSingh]

http://sikhcybermuseum.com/history/ForsterObservation.htm

George Foster-1783

The Seicks do not seem to be at all rigorous in their requisitions from Mussulmen Proselytes, who, if they abstain from eating Beef Flesh, which is held in as much Abhorrence by the Seicks as by the Hindoos, they are indulged in every other article.

[shastarSingh]

http://sikhcybermuseum.com/history/MemorandumGrifiths.htm

John Griffiths -1794

The Seiks receive Proselytes of almost every Cast, a point in which they: differ most materially from the Hindoos. To initiate Mahommedans into their mysteries, the prepare a Dish of Hog's legs, which the Converts are obliged to partake of previous to admission. They have forbid absolutely the use of the Hookah, but they are as liberal in the use of Bang, and Ophiam, as their Neighbours. They are not prohibited the use of Animal food of any kind, excepting Beef, which they are rigidly scrupulous in abstaining from. They never shave either Head or Beard; They sometimes wear yellow, but the prevailing Colour of their Cloths is deep blue; They make their Turbans capaciously large, over which they frequently wear a piece of pliable Iron Chain or Network.

[shastarSingh]

Malcolm wrote 'Sketch of the Sikhs' in 1812. It can be downloaded at

https://archive.org/details/sketchofsikhssin00malcrich

In it he writes that the prejudice of the Sikhs regarding the killing of cows is stronger than Hindus

[shastarSingh]

Beef was banned in Maharaja Ranjit Singh's empire.

https://www.sikhsangat.com/index.php?/topic/88068-diet-of-maharaja-ranjit-singh-and-sikhs-of-that-time/

Osborne met Maharaja Ranjit Singh in 1838. He writes:

1.  26th June.—This morning, at sunrise, ordered our elephants, and went out to try and relieve the monotony of our life by a few hours' shooting. Proceeded straight to a
rumna, or preserve, of the Maharajah's, which we supposed to abound in wild hog, hares, and black partridges. The Sihks, in
contradiction to the religious tenets of most of the other castes in India, are very fond of pork, and Runjeet cultivates grain and sugar- cane round this preserve for the wild hog who frequent it to feed upon. Beef is as much a forbidden food in the Punjab as pork is in Hindostan to the natives ; and to kill a cow across the Sutlege would subject the perpe-trator of the deed to almost certain death.
We found a considerable quantity of wild hog, and a few black partridges, in the rumna, and had altogether two hours' very
tolerable shooting.

[GurjantGnostic]

9 hours ago, shastarSingh said:

Malcolm wrote 'Sketch of the Sikhs' in 1812. It can be downloaded at

https://archive.org/details/sketchofsikhssin00malcrich

In it he writes that the prejudice of the Sikhs regarding the killing of cows is stronger than Hindus

A lot of the commentary in this source is speculative. 

[shastarSingh]

13 hours ago, GurjantGnostic said:

A lot of the commentary in this source is speculative. 

Yes.

Malcolm's information about Guru Sahib may not be totally correct. But his information about Sikhs is pretty nice.

https://www.thesikhencyclopedia.com/sikh-scriptures-and-literature/sri-guru-granth-sahib-and-guru-gobind-singhs-bani/sketch-of-the-sikhs/

Malcolm was able to get firsthand information about the Sikhs when he accompanied, in 1805, Lord Lake`s army in pursuit of Jasvant Rao Holkar into the Sutlej Yamuna Divide.

[shastarSingh]

https://twitter.com/Pashz7/status/1465689676367286277?s=20&t=d40myf98GRcxkRBKHM6IUA

[shastarSingh]

https://www.quora.com/Did-Ranjit-Singh-ban-beef