user2962: 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?


user703: 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.


user14829: 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.
A History of Chess - Page 70
A History of Chess - Cover

2962: <p>My question is about the history of the pawn promotion rule (promotion to a queen). </p>

<blockquote>
  <p>What is the earliest existing text (authentic written document in any language) which mentions the pawn promotion rule?</p>
</blockquote>
 703: <p>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.</p>

<p>So, a couple of websites mentioning the same year: <strong>1475</strong>. This is when pawn was able to be promoted to a queen.</p>

<p>For example <a href="http://www.learnchesswithsam.com/chess.html" rel="nofollow">this one tells</a>:</p>

<blockquote>
  <p>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.</p>
  
  <p>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.</p>
</blockquote>

<p>And simmilar <a href="http://www.britannica.com/EBchecked/topic/447416/pawn-promotion" rel="nofollow">this one</a>:</p>

<blockquote>
  <p>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</p>
</blockquote>

<p>Also interesting "fact" about the promotion to a queen can be <a href="http://www.chess-poster.com/english/notes_and_facts/did_you_know.htm" rel="nofollow">found here</a></p>

<blockquote>
  <p>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.</p>
</blockquote>
 14829: <p>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.</p>

<p><a href="https://i.stack.imgur.com/IT1tu.jpg" rel="nofollow noreferrer">A History of Chess - Page 70</a>
<a href="https://i.stack.imgur.com/vbEkw.jpg" rel="nofollow noreferrer">A History of Chess - Cover</a></p>
