Our rabbis taught a story about Acher:
Once, he was riding on a horse on Shabbat, and Rabbi Meir was walking after him, in order to learn Torah from his mouth.
He said, “Meir, turn back. Because I’ve already measured by my horse’s steps that this is the boundary line for Shabbat travel.”
Meir replied, “You, too, turn back!”
He said, “Haven’t I already told you? I heard behind the curtain that the verse, ‘Return you wayward children!’ applies to everyone - except Acher.”