Sefer Chasidim Siman 225
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
חכם אחד צוה לבנו שלא יהנה יותר מדאי בעולם הזה שלא יעברו עליו שמנה ימים בלא תענית ואפילו על שונאו יתפלל שיעבוד להקב"ה:
Sefaria Community Translation
There was one wise man who commanded his son that he shouldn't derive too much pleasure from this World and no eight days should pass for him without a fast and that even for his enemy he should pray that he should serve the Holy One, blessed be He.