Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) narrates: In the beginning of Islam, there was a concession regarding "water for water" (i.e., the ruling that ghusl is obligatory only upon the emission of semen), then this was prohibited. (Imam Ibn Hibban, may Allah have mercy on him, says:) This narration has been transmitted by Mu'ammar from Zuhri, which has been narrated by Ghundar. He says: Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) narrated this hadith to me. The same narration has been transmitted by 'Amr bin Khalid from Zuhri. In it, he says: A person whom I am pleased with narrated this hadith to me, and he narrated it from Sayyiduna Sahl bin Sa'd. So, it is possible that Zuhri himself heard this narration from Sayyiduna Sahl bin Sa'd, as Ghundar has stated, and Zuhri may have heard this narration from a person whom he was pleased with, and that person narrated it from Sayyiduna Sahl bin Sa'd. So, once he narrated it directly from Sayyiduna Sahl bin Sa'd, and another time he narrated it from the person whom he was pleased with, from Sayyiduna Sahl bin Sa'd. I investigated the chains of this narration to find if there was anyone who narrated this narration from Sayyiduna Sahl bin Sa'd, but I did not find anyone in the world except Abu Hazim. So, it is possible that the person about whom Zuhri said: "A person whom I am pleased with narrated this hadith to me," he narrated this hadith from Sayyiduna Sahl bin Sa'd, and that person is Abu Hazim, who narrated this narration from Sayyiduna Sahl.