Musannaf Ibn Abi Shayba 13:3142

Abu Bakr narrated to us, he said: Abd al-Rahman ibn Mahdi narrated to us, from Sa'id ibn Zayd, from Abu Abd al-Rahman al-Shaqari, regarding a man who sells a debt for a deferred term, then the buyer sells it to another man: "May its owner, who sold it, buy it?" He said: "If there is no collusion (muwalah) in it, then there is no harm."