I said, "Messenger of Allah, I am a man who deals in trade. What is permitted in such transactions and what is forbidden?"He replied, "My nephew, when you buy something, do not sell it until you have taken possession of it."
قلت: يا رسول الله، إني رجل أشتري بيوعا، فما يحل منها وما يحرم؟ قال: يا ابن أخي، إذا اشتريت بيعا فلا تبعه حتى تقبضه.
Ibn Jarud narrated it in Muntaqa (602), Ibn Hibban (4983), and Daraqutni (2822), all of them through routes from Hammam bin Yahya, who said, "Yahya bin Abu Kathir narrated to us, Yaala bin Hakeem narrated to us, who said, Yusuf bin Mahak narrated to us, from Abdullah bin Isma, from Hakeem bin Hizam," and he related it. The wording given is Ibn Jarud's, and the wording of the other two is similar to it. Its isnad is hasan because of Abdullah bin Isma, and his hadith is hasan.Hisham Dastawai corroborated Hammam bin Yahya, narrating it from Yahya bin Abu Kathir with his isnad. Ibn Jarud and Bayhaqi (5/313) narrated it through his route, except that the latter did not mention Yaala bin Hakeem between Yahya bin Abu Kathir and Yusuf bin Mahak. For this reason he followed it up by saying, "Yahya bin Abu Kathir did not hear it from Yusuf, rather he heard it from Yaala bin Hakeem, from Yusuf."Likewise Shayban corroborated him, narrating it from Yahya bin Abu Kathir, from Yaala bin Hakeem, with his isnad. Ibn Jarud and Bayhaqi narrated it through his route. Bayhaqi said, "This is a hasan, connected isnad." He also said, "Likewise Hammam bin Yahya and Aban bin Attar narrated it from Yahya bin Abu Kathir."I say, the hadith of Abu Aban Attar was narrated by Daraqutni (2820).Once you know this, know that it has come in the Sunan and Masanid, Abu Dawud (3503), Tirmidhi (1232), Nasai (4613), Ibn Majah (2187), Ahmad (15312), and others, from Yusuf bin Mahak, from Hakeem bin Hizam, and he related it. This is a disconnected isnad, for Yusuf bin Mahak did not hear from Hakeem bin Hizam, and what has come in some narrations explicitly stating that he heard directly from him amounts to nothing. Bukhari and others have affirmed that Yusuf bin Mahak did not hear from Hakeem bin Hizam.So Tirmidhi's statement, "This is a hasan hadith," is not correct, for a disconnected isnad cannot be hasan, unless his statement is understood to mean that it is hasan through other routes, since he was passing judgment on the hadith itself, not on the isnad.