Sayyiduna Abu Rafi' (may Allah be pleased with him) narrates: After the passing of the Prophet (peace and blessings be upon him), we found a document in the sheath of the Prophet's (peace and blessings be upon him) sword, in which was written: "In the name of Allah, the Most Gracious, the Most Merciful. Separate the beds of boys and girls, and of brothers and sisters, at the age of seven; and beat your children for the prayer at the age of seven. Accursed, accursed is the one who claims to belong to other than his own people (the narrator is unsure; perhaps the words are:) or attributes himself to other than his freeing masters. And accursed is the one who seizes any piece of land." (The narrator says:) By this the Prophet (peace and blessings be upon him) meant the one who seizes something from the roads of the Muslims.
Al-Bazzar recorded it; its chain mentions that Ghassan bin Ubaydullah narrated it from Yusuf bin Nafi', and I have not found anyone who mentions either of them.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 1627