"The Messenger of Allah said: 'When the two circumcised parts meet, and (the tip of the penis) disappears, then bath is obligatory.'" (Using translation from Ibn Mājah 611)
قَالَ رَسُولُ اللهِ ﷺ إِذَا الْتَقَتِ الْخِتَانَانِ وَتَوَارَتْ الْحَشَفَةُ فَقَدْ وَجَبَ الْغُسْلُ