Reference to return substitutions is found in:
The provision as it is printed, and everything on Ruleside that turns on it.
The use of return substitutions is only permitted in youth, veterans, disability and grassroots football, subject to the agreement of the national football association, confederation or FIFA.
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.