My question is about the history of the pawn promotion rule (promotion to a queen).
What is the earliest existing text (authentic written document in any language) which mentions the pawn promotion rule?
According to H.J.R. Murray (in A History of Chess, 1913), the pawn promotion rule (specially named as 'shatpada' or six steps) is already found in the very first known ancestry of chess: chaturanga (an ancient indian four-handed dice game whose pieces were King, Elephant, Chariot, Horse and Pawn for each one of the four armies). Chaturanga exists in this form at least since the 7th century of our era. The subsequent forms of games related to chaturanga, including our western chess, have employed several different ways to promote pawns through the centuries (only to queen - or similar, like vizir or counsellor; only if the pawn reaches the 8th row at selected ranks - for example not in the 'e', 'b' or 'g' files; only to a previously captured piece; only to the piece originally related to the rank; etc), but this feature has been always present.
I did not want to post this as an answer, due to the lack of actual proof (link to a site, can not be considered as a normal proof). But looking that it was not answered for few days, I decided to show what I have and if someone will be able to find anything better - he will improve/write new.
So, a couple of websites mentioning the same year: 1475. This is when pawn was able to be promoted to a queen.
For example this one tells:
What happened in 1475? Until then, there was no Queen... The King had a counselor who could move diagonally one square at a time. One other major difference concerned promotion. A pawn, reaching the 8th rank, could only become a counselor.
Around 1475, the counselor underwent a sex-change and emerged as the powerful Queen with whom we are all familiar. Promotion rules changed to the modern European version. Another factor played an important role in stabilizing chess at this point in time: the printing press! Books were written and more freely distributed and within 100 years, modern chess (chess, as we know it) was an established fact with only minor changes (castling, promotion to more-than-one Queen, en passant) occurring through the 19th century.
And simmilar this one:
that became popular after 1475. Until then the counselor was limited to moving one square diagonally at a time. And, because a pawn that reached the eighth rank could become only a counselor, pawn promotion was a relatively minor factor in the course of a game. But under the new rules the counselor underwent a sex change and gained vastly increased mobility to become the most powerful
Also interesting "fact" about the promotion to a queen can be found here
In the 15th century, promotion to allow more than one Queen was considered improper because it symbolized adultery. In Spain and Italy in the 17th century, the Pawn could only be promoted to the rank of Queen. In France and Germany, promotion was limited to any piece which had been lost. In some countries a player could promote a Pawn to an enemy piece so as to force stalemate. The current law in Pawn promotion was established at the first International Tournament in 1851.