عَنْ عَمْرِو بْنِ شُعَيْبٍ عَنْ جَدِّهِ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: إِذَا الْتَقَى الْخِتَانَانِ وَتَوَارَتِ الْحَشْفَةُ فَقَدْ وَجَبَ الْغُسْلُ
It is narrated from Sayyiduna Abdullah bin Amr bin Aas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: When the two circumcised parts meet and the glans becomes concealed, then ghusl becomes obligatory.