The Messenger of Allah ﷺ only permitted that as a concession for the people in the early days of Islam due to the scarcity of garments. Then he commanded full bathing and forbade that practice.Abu Dawud said, He means the ruling that water is required only after the emission of fluid.
إن رسول الله ﷺ إنما جعل ذلك رخصة للناس في أول الإسلام لقلة الثياب، ثم أمر بالغسل، ونهى عن ذلك. قال أبو داود: يعني الماء من الماء.
Abu Dawud (214) recorded it from the hadith of Amr bin Harith, from Ibn Shihab Zuhri, who said, "Someone I trust told me that Sahl bin Saad Saadi informed him that Ubayy bin Kaab informed him," and then he mentioned the hadith. Its chain is connected, except that it contains an unnamed man who was not identified. Ibn Khuzayma (1/114) said, "This man whom Amr bin Harith did not name appears to be Abu Hazim Salama bin Dinar, because Mubashshir bin Ismail narrated this report from Abu Ghassan Muhammad bin Mutarrif, from Abu Hazim, from Sahl bin Saad."What Ibn Khuzayma mentioned was narrated by Abu Dawud (215), who said, Muhammad bin Mihran Bazzar Razi told us, Mubashshir Halabi told us, with the same wording. Bayhaqi said, after narrating it through Abu Dawud's route from Amr bin Harith, from Ibn Shihab, who said, "Someone I trust told me," "We have also narrated it through another chain, connected and sahih, from Sahl bin Saad." This is what he narrated from the hadith of Musa bin Harun, who said, Muhammad bin Mihran Jammal told us, and through the route of Abu Dawud, who said, Muhammad bin Mihran Razi told us, Mubashshir Halabi told us, from Muhammad Abu Ghassan, from Abu Hazim, from Sahl bin Saad, who said, "Ubayy bin Kaab told me that the ruling they used to give, that water is only required after water, was a concession that the Messenger of Allah had granted at the beginning of Islam, and then he later commanded ghusl." In the narration of Musa bin Harun it reads, "Then he commanded us to perform ghusl afterward." Sunan al-Kubra (1/165–166).I say, the men of this chain are trustworthy except Mubashshir bin Ismail Halabi, who is truthful. It is possible that Zuhri heard it from Abu Hazim, then hesitated or was uncertain about his name and said, "Someone I trust told me," and then later had the opportunity to hear it from Sahl himself. Yunus narrated from Zuhri that he said, "Sahl told me," and in another version he said, "Sahl bin Saad Saadi said, Ubayy bin Kaab informed us," and then he mentioned the hadith.This last version was recorded by Ibn Majah (609), who said, from Muhammad bin Bashshar, Uthman bin Umar told us, Yunus informed us, with this wording. Tirmidhi also recorded it (110), saying, Ahmad bin Mani told us, Abdullah bin Mubarak told us, Yunus bin Yazid informed us, from Zuhri, from Sahl bin Saad, and he mentioned the same. Tirmidhi said, "Mamar also informed us, from Zuhri, with this same chain, with the same wording." And he said, "This hadith is hasan sahih."So both Yunus bin Yazid and Mamar narrated from Zuhri, from Sahl bin Saad, without any intermediary between them. In all cases, the chain is sahih. This establishes that the hadith "water is only required after water" was abrogated.Tirmidhi said, "The rule that water is only required after water applied only at the beginning of Islam, and was later abrogated. This is how more than one of the companions of the Prophet narrated it, among them Ubayy bin Kaab and Rafi bin Khadij. The practice among most scholars is that if a man has intercourse with his wife in the vagina, ghusl becomes obligatory on both of them even if neither of them ejaculates." End of quote.I say, as for the hadith of Ubayy bin Kaab, its sourcing has already been given. As for the hadith of Rafi bin Khadij, it is daif. Imam Ahmad recorded it in his Musnad (17288), saying, Qutayba bin Saeed told us, saying, Rushdin bin Saad told us, from Musa bin Ayub Ghafiqi, from one of the sons of Rafi bin Khadij, from Rafi bin Khadij, who said, "The Messenger of Allah called out to me while I was on top of my wife. I got up without ejaculating, so I performed ghusl and went out to the Messenger of Allah, and I told him that he had called me while I was on top of my wife, so I got up without ejaculating and performed ghusl. The Messenger of Allah said, 'There is no need for you, water is only required after water.'" Rafi said, "Then the Messenger of Allah later commanded us to perform ghusl." End of quote.Rushdin bin Saad, with the ra vowelled with a kasra and the dal unvowelled, Mahri, Abul-Hajjaj Masri, Ibn Main said of him, "He is of no account." Abu Hatim said, "His hadith is objectionable." Nasai said, "His hadith is to be discarded." Abu Dawud, Daraqutni, and others also declared him daif. Moreover, the chain contains an unidentified son of Rafi bin Khadij. As for Musa bin Ayub, Ibn Main said of him, "His hadith is objectionable."Haythami mentioned this in Majma al-Zawaid (1/264–265), attributing it to Ahmad and to Tabarani in Al-Kabir, and said, "It contains Rushdin bin Saad, who is daif."I say, Tabarani recorded it in Al-Kabir (4347) and in Al-Awsat (6509), and named the son of Rafi bin Khadij as Sahl, saying, "No one narrated from Sahl except Musa bin Ayub Ghafiqi, and Rushdin narrated it alone." We could not find any biographical entry for Sahl bin Rafi bin Khadij.I say, on this subject there is also what was narrated by Abu Hurairah and Bilal, though none of it has been established as sound.