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."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11350
Kathir bin Abdullah narrates from his father, from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "Reconciliation between Muslims is permissible, except a reconciliation that makes the unlawful lawful and the lawful unlawful."
Abu Amir al-Aqadi also narrated it likewise from Kathir bin Abdullah, and reliance is on his narration, for Muhammad bin al-Hasan bin Zabalah is utterly da'if (weak); and the narration of Kathir bin Abdullah bin Amr bin Awf al-Muzani, when joined to the one before it, the two strengthen each other.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11352
Idris al-Awdi (may Allah have mercy on him) said that Sa'id bin Abi Burdah (may Allah have mercy on him) brought out a document and said: This is the letter that Sayyiduna Umar (may Allah be pleased with him) sent to Sayyiduna Abu Musa (may Allah be pleased with him). In it was written: "Reconciliation between people is permissible, except a reconciliation that makes the unlawful lawful and the lawful unlawful; that is not permissible."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11353
Abu Salamah (may Allah have mercy on him) said: The wife of Abd al-Rahman (may Allah be pleased with him) was given a settlement for her share, a quarter of the eighth, for 80,000.
This is understood to mean that she knew the amount of her share.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11355
Salim (may Allah have mercy on him) said: When a man was owed gold or silver by Ibn Umar (may Allah be pleased with them both), he would give him the choice at the time of repayment: "Which of the two kinds do you prefer?" Then he would pay him at the people's rate of exchange, or he would exchange (the money) and then pay him. When the man accepted that, Abdullah (may Allah be pleased with them both) saw no harm in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11356
Sa'id (may Allah have mercy on him), the freed slave of Hasan bin Ali (may Allah be pleased with him), said: Ibn Umar (may Allah be pleased with them both) owed me some dirhams. I asked him for them, and he said: When I receive my stipend I will pay you. Sa'id said: When he received 100 dinars, I came to him. He said to his servant: Take these dinars to the market; when a price is set for them, give him his dirhams from it; and if he prefers that you sell them for dirhams, then do so and give him his dirhams.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11357