The Messenger of Allah ﷺ said, "If any of you touches his private part with his hand, with no covering or barrier between them, let him perform ablution."
قال رسول الله ﷺ: إذا أفضى أحدكم بيده إلى فرجه، وليس بينهما ستر ولا حجاب فليتوضا.
Tabarani narrated it in al-Awsat (1871) and al-Saghir (110), and Ibn Hibban (1118), all of them through Ahmad bin Saeed Hamdani, who said, "Asbagh bin Faraj narrated to us, who said, Abdul-Rahman bin Qasim narrated to us, from Nafi bin Abu Naeem Qari, from Saeed Maqburi, from Abu Hurairah," and he related the hadith. Its chain is hasan because of Nafi bin Abu Naeem Qari, for he is truthful.This hadith is well known through the narration of Yazid bin Abdul-Malik Nawfali, who is daif, and through his route it was narrated by Imam Ahmad (8404), Bazzar in Kashf Astar (286), Bayhaqi (1/133), and Ibn Hibban (1118), who paired him with Nafi bin Abu Naeem.Hafiz said in al-Talkhis (1/126), "Ibn Abdul-Barr said, this hadith used to be known only through the narration of Yazid (bin Abdul-Malik), until Asbagh narrated it from Ibn Qasim, from Nafi bin Abu Naeem and Yazid together, from Maqburi, so the hadith was established as sound."Ibn Sakan said, "It is the best of what has been narrated on this subject."Hakim recorded it (1/138) through the route of Nafi and graded it sahih. Hafiz quoted remarks from the scholars regarding Nafi bin Abu Naeem, and the conclusion is that his hadith is hasan.The hadith has other chains, but they are all daif.