360. hadíth
وَ إِنَّمَا سُمِّيَ يَوْمَ اَلتَّرْوِيَةِ لِأَنَّهُ لَمْ يَكُنْ بِعَرَفَاتٍ مَاءٌ وَ كَانُوا يَسْتَقُونَ مِنْ مَكَّةَ مِنَ اَلْمَاءِ لِرَيِّهِمْ وَ كَانَ يَقُولُ بَعْضُهُمْ لِبَعْضٍ تَرَوَّيْتُمْ تَرَوَّيْتُمْ فَسُمِّيَ يَوْمَ اَلتَّرْوِيَةِ لِذَلِكَ ».
The Day of Tarwiyah (8th of Dhul-Hijjah) was named so because there was no water in Arafat, and people would bring water from Makkah to quench their thirst. They would say to one another, 'Have you provided water for yourselves? Have you provided water for yourselves?' Thus, it was named the Day of Tarwiyah for this reason.