Infinite loop in the on_message method

Question

Hello, everyone. I have an infinite loop on my Discord bot, but I don’t know how to fix it.

import discord
import asyncio
import strings_codes #minha classe de string e códigos
import auxiliary_functions #minha classe de funções auxiliares


client = discord.Client()


@client.event
async def on_ready():
    await client.send_message(client.get_channel(strings_codes.test_channel_id), strings_codes.welcome_message)


@client.event
async def on_message(message):
        lower_command = message.content.lower()

        if lower_command.startswith('!'):
            await client.send_message(message.channel, auxiliary_functions.switch_command(message))
        else:
            await client.send_message(message.channel, strings_codes.invalid_commands['wrong_prefix'])

client.run(strings_codes.token)

The method on_ready() calls the method send_message() with the greeting message and triggers the method on_message(), which also has the method send_message() in its scope, thus causing the bot to endlessly capture its own message. I saw the code of many people and they did not need to put a condition to trigger the event that has the method on_message(). How do I fix it? Thank you.