Sunan an-Nasa'i 157
سنن النسائي#157Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، عَنْ شُعْبَةَ، قَالَ أَخْبَرَنِي سُلَيْمَانُ، قَالَ سَمِعْتُ مُنْذِرًا، عَنْ مُحَمَّدِ بْنِ عَلِيٍّ، عَنْ عَلِيٍّ، قَالَ اسْتَحْيَيْتُ أَنْ أَسْأَلَ النَّبِيَّ، صلى الله عليه وسلم عَنِ الْمَذْىِ مِنْ أَجْلِ فَاطِمَةَ فَأَمَرْتُ الْمِقْدَادَ بْنَ الأَسْوَدِ فَسَأَلَهُ فَقَالَ " فِيهِ الْوُضُوءُ " .
It was narrated that 'Ali said:"I felt too shy to ask the Messenger of Allah (ﷺ) about prostatic fluid because of Fatimah, so I told Al-Miqdad bin Al-Aswad to ask about it, and he (the Prophet (ﷺ)) said: 'Perform Wudu' for that
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 1:158