Reference to return substitutions is found in:
The provision as it is printed, and everything on Ruleside that turns on it.
A ‘return substitute' is a player who has already played in the match and has been substituted (a substituted player) and later in the match returns to play by replacing another player.
Verdicts that turn on it 1
Walk the tree to any of these and this clause is part of the answer.
The Laws of the Game are published by The IFAB and quoted here for the purpose of explaining the decisions on this site. Ruleside is not affiliated with The IFAB or FIFA. Every clause of Notes and modifications that Ruleside cites.