Al-Kāfi - Volume 6 > Al-Tila’ (The One-Third Juice (grape juice) that has Remained after the Evaporation of the other Two-Thirds)
Hadith #5

ابْنُ أَبِي عُمَيْرٍ عَنْ عُمَرَ بْنِ يَزِيدَ قَالَ قَالَ أَبُو عَبْدِ اللَّهِ ( عليه السلام ) إِذَا كَانَ يَخْضِبُ الْإِنَاءَ فَاشْرَبْهُ .

5. Ibn abu ‘Umayr has narrated from ‘Umar ibn Yazid who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said, ‘When two-thirds of juice (grape juice) is evaporated (because of boiling) then you can drink it.’”