Kathir bin 'Amr bin 'Awf Al-Muzani narrated from his father, from his grandfather, that the Messenger of Allah (ﷺ) said:"Reconciliation is allowed among the Muslims, except for reconciliation that makes the lawful unlawful, or the unlawful lawful. And the Muslims will be held to their conditions, except the conditions that make the lawful unlawful, or the unlawful lawful

English translation · Jami' at-Tirmidhi