Is there a rule that doesn't allow adjustment during the opponents time?

Question

While playing a tournament, I adjusting my pieces several times during my opponent's time. He claimed a win for the same. Can anyone explain how this rule works and why is it there?

Answer 1

I think this FIDE rules section explains that:

Article 6.2

d. Only the player whose clock is running is allowed to adjust the pieces.

According to Article 4.2, a player should announce "j’adoube" (I adjust) before adjusting pieces on the board, providing only the player having the move may adjust one or more pieces on their squares (i.e. player in turn with clock still running).

In actual games usually the arbiter only issues verbal warning about adjusting pieces only in respective player's turn. But keep in mind you should avoid distracting the opponent, i.e. obstructing their view on the board when it's opponent's turn to make a move, since Article 4.8 applies if a player decides repeating disruptive behavior from his/her opponent, without announcing to adjust the pieces first:

A player forfeits his right to claim against his opponent’s violation of Articles 4.1 – 4.7 once the player touches a piece with the intention of moving or capturing it.

Related issue:

Adjusting in ones turn only

Answer 2

In your case, the relevant rule is here :

4.2
Provided that he first expresses his intention (for example by saying “j’adoube” or “I adjust”), only the player having the move may adjust one or more pieces on their squares.

[...]

4.8
A player forfeits his right to claim against his opponent’s violation of Articles 4.1 – 4.7 once the player touches a piece with the intention of moving or capturing it.

As for why, I believe that adjusting your pieces while your opponent is thinking is very disruptive, especially if it happened several times during the game. It just breaks his focus. During your opponent's turn, you should let him focus as much as they want. It could also be very unfair if you adjust your pieces while your opponent doesn't have much time, since you are using their time at their detriment.