Chapter on Fasting with Authorization
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 2|Chapter 31
وَ قَدْ رُوِيَ أَنَّهُ: «يُغْتَسَلُ فِي لَيْلَةِ سَبْعَ عَشْرَةَ ».
It has also been narrated that: "One should perform the ritual bath (ghusl) on the night of the seventeenth."
- Ṣaḥīḥ al-Faqīh