Language:
كتاب الغسل
5  
Bathing (Ghusl)
(9)
Chapter: Can a Junub (a person who has yet to take bath after the sexual act or wet dream) put his hands in a pot (containing water) before washing them if they are not polluted with a dirty thing except Janaba?
(9)
باب هَلْ يُدْخِلُ الْجُنُبُ يَدَهُ فِي الإِنَاءِ قَبْلَ أَنْ يَغْسِلَهَا إِذَا لَمْ يَكُنْ عَلَى يَدِهِ قَذَرٌ غَيْرُ الْجَنَابَةِ
Sahih al-Bukhari 262

Narrated `Aisha:

Whenever Allah's Messenger (ﷺ) took a bath of Janaba, he washed his hands first.

حَدَّثَنَا مُسَدَّدٌ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا اغْتَسَلَ مِنَ الْجَنَابَةِ غَسَلَ يَدَهُ‏.‏
Reference : Sahih al-Bukhari 262
In-book reference : Book 5, Hadith 15
USC-MSA web (English) reference : Vol. 1, Book 5, Hadith 262
  (deprecated numbering scheme)