(51) The Book of Drinks
كتاب الأشربة
(53) Chapter: What Kind of Thickened Grape Juice is Permissible to Drink and What Kind is Not Permitte
(53) باب ذِكْرِ مَا يَجُوزُ شُرْبُهُ مِنَ الطِّلاَءِ وَمَا لاَ يَجُوزُ ‏‏
Sunan an-Nasa'i 5725 
It was narrated that Bushair bin Al-Muhajir said:
"I asked Al-Hasan about juice that has been cooked. He said: 'That which has been cooked until two-third of it has gone and one-third is left.'"
أَخْبَرَنَا سُوَيْدٌ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ بَشِيرِ بْنِ الْمُهَاجِرِ، قَالَ سَأَلْتُ الْحَسَنَ عَمَّا يُطْبَخُ مِنَ الْعَصِيرِ قَالَ مَا تَطْبُخُهُ حَتَّى يَذْهَبَ الثُّلُثَانِ وَيَبْقَى الثُّلُثُ ‏.‏
Grade :  Hasan (Darussalam)
Reference : Sunan an-Nasa'i 5725
In-book reference : Book 51, Hadith 187
English translation : Vol. 6, Book 51, Hadith 5728