Sunan Ibn Majah, Book 1, Hadith 652 (In-Book) ⓘ
Ubayy bin Ka'b said: "That was a concession that was granted in the early days of Islam, then we were commanded to have a bathe after that."
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ، أَنْبَأَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، قَالَ قَالَ سَهْلُ بْنُ سَعْدٍ السَّاعِدِيُّ أَنْبَأَنَا أُبَىُّ بْنُ كَعْبٍ، قَالَ إِنَّمَا كَانَتْ رُخْصَةً فِي أَوَّلِ الإِسْلاَمِ ثُمَّ أُمِرْنَا بِالْغُسْلِ بَعْدُ .
also referenced under: Hadith 609 (Reference) & Volume 1, Book 1, Hadith 609 (DarusSalam)