Reconciliation between Muslims is permissible, except that which makes the lawful unlawful

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Reconciliation between Muslims is permissible." A supporting report (shahid) for this hadith is the hadith of Sayyiduna Amr bin Awf (may Allah be pleased with him), and through it this (meaning) is known:

Kathir bin Abdullah narrates from his father, from his grandfather Sayyiduna Amr bin Awf (may Allah be pleased with him), who said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Reconciliation between Muslims is permissible, except a reconciliation that makes something lawful unlawful or makes something unlawful lawful; and Muslims are bound by their (agreed) conditions, except a condition that makes something lawful unlawful."

The son of Sayyiduna Ka'b bin Malik (may Allah be pleased with him) narrates from his father that the Messenger of Allah (peace and blessings be upon him) placed a restriction on the property of Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) (because of debt), and sold it to pay off the debt that he owed.
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that during the time of the Messenger of Allah (peace and blessings be upon him) there was a man who used to buy and sell, and there was some weakness in his judgement (that is, in his intellect or power of decision). His family came to the Prophet (peace and blessings be upon him) and said: O Prophet of Allah, place a restriction (on trading) on so-and-so, for he makes deals and there is weakness in his understanding. So the Prophet (peace and blessings be upon him) called him and forbade him from buying and selling. He said: O Prophet of Allah, I cannot do without trading. So he (peace and blessings be upon him) said: "If you are not going to give up trading, then say (when making a deal): 'Ha wa la khilabah' (Here it is, and let there be no deception)."
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.