[Tayab]

If I got correctly, this is what you want to do basically. Read the comments carefully.

pawn Код:

//Create a variable where you'll store wheather the chat should be blocked or not.
new ChatBlocked[MAX_PLAYERS];

// Un-Block the chat when player connects
public OnPlayerConnect(playerid)
{
    ChatBlocked[playerid] = 0;
    return 1;
}
public OnPlayerText(playerid,text[])
{
    //check if the player is blocked for getting chats from all players
    for(new i = 0; i < MAX_PLAYERS; i++)
    {
        if(ChatBlocked[i] == 1)
        {
            return 0;
        }
        else SendClientMessageToAll(GetPlayerColor(playerid),text);
    }
    return 1;
}
//now you can make command to (un)block the chat for player.
CMD:chatblock(playerid,params[])
{
    new pID,value;
    if(!IsPlayerAdmin(playerid)) return SendClientMessage(playerid,0xCCCCCCCC,"You're not a RCON admin.");
    if(sscanf(params,"ud",pID,value)) return SendClientMessage(playerid,0xFFFFFFFF,"USAGE: /chatblock [playerid] [value]");
    if(!IsPlayerConnected(pID)) return SendClientMessage(playerid,0xCCCCCCCC,"Player is not connected.");
    if(!(-1 < value < 2)) return SendClientMessage(playerid,0xCCCCCCCC,"Invalid value [0-1]");
    ChatBlocked[playerid] = value;
    return 1;
}