Al-Kāfi - Volume 7 > One who Does not have Testimony, then Oath is Turned on Him
Hadith #5

5- عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ هِشَامِ بْنِ سَالِمٍ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) قَالَ يُرَدُّ الْيَمِينُ عَلَى الْمُدَّعِي.

5. Ali ibn Ibrahim has narrated from his father from ibn abu ‘ Umayr from Hisham ibn Salim who has narrated the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that the oath can be turned to the plaintiff.”