كتاب الطهارة
1  
The Book of Purification
(8)
Chapter: Taking Ghusl (bath) And the precepts regarding Sexual Impurity
(8)
باب الغسل وحكم الجنب
Bulugh al-Maram 120
Narrated Maimuma (rad):
Allah’s Messenger (ﷺ) poured water over his private parts and washed them with his left hand. He then struck his hand against the earth.
وَلَهُمَا فِي حَدِيثِ مَيْمُونَةَ: { ثُمَّ أَفْرَغَ عَلَى فَرْجِهِ, فَغَسَلَهُ بِشِمَالِهِ, ثُمَّ ضَرَبَ بِهَا اَلْأَرْضَ }

Reference : Bulugh al-Maram 120
In-book reference : Book 1, Hadith 145
English translation : Book 1, Hadith 129