@client.command()
async def say(ctx, *args):
embed = discord.Embed(description=f" ".join(args), color=0x8A2BE2)
embed.set_image(url="url")
await ctx.send(embed=embed)
*args
тоже можно убрать в таком случаеasync def say(ctx, phrase):
embed = discord.Embed(description=phrase, color=0x8A2BE2)
!say "Привет,
мир"