وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ إِذَا جَاوَزَ الْخِتَانُ الْخِتَانَ فَقَدْ وَجَبَ الْغُسْلُ ‏.‏

Yahya related to me from Malik from Nafi that Abdullah ibn Umarused to say, "When the circumcised part passes the circumcised part,ghusl is obligatory." Translation Not Available

Book Ref: Muwatta Imam Malik Book 2 Hadith 107
Web Ref:  Muwatta Imam Malik Book 2 Hadith 77