Абу Дауд
There are commentaries on touching the male genital by oneself in various narrations of Hadith. One example is the hadith of Basrah bint Safwaan, who heard Muhammad say: "Whoever touches his private parts, let him do wudoo (washing)’." (Narrated by Abu Dawood, al-Tahaarah, 154. al-Albaani said in Saheeh Sunan Abi Dawood, no. 166, it is saheeh).