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

مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عَلِيِّ بْنِ الْحَكَمِ عَنْ مُعَاوِيَةَ بْنِ وَهْبٍ قَالَ سَأَلْتُ أَبَا عَبْدِ اللَّهِ ( عليه السلام ) عَنِ الْبُخْتُجِ فَقَالَ إِنْ كَانَ حُلْواً يَخْضِبُ الْإِنَاءَ وَ قَالَ صَاحِبُهُ قَدْ ذَهَبَ ثُلُثَاهُ وَ بَقِيَ الثُّلُثُ فَاشْرَبْهُ .

6. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from Ali ibn al-Hakam from Mu‘awiyah ibn Wahab who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about al-Bakhtaj (boiled juice). He (the Imam) said, ‘If it is sweet with an indication of two-thirds being evaporated and the owner also says that two- thirds have been evaporated, only one-third has remained, then you can drink it.’”