يُسَنُّ الِاغْتِسَالُ لِأَرْبَعَةِ أَشْيَاءَ: صَلَاةِ الْجُمُعَةِ، وَصَلَاةِ الْعِيدَيْنِ، وَلِلْإِحْرَامِ، وَلِلْحَاجِّ فِي عَرَفَةَ بَعْدَ الزَّوَالِ
1. For Jumu'ah prayer.
2. For the two Eid prayers.
3. For entering Ihram.
4. For the Hajj pilgrim at Arafah after midday.
Ihram here is the ritual state, not merely changing clothes.