(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 5723 
It was narrated that Sa'eed bin Al-Musayyab said:
"When At-Tila' (thickened grape juice) has been cooked and reduced to one-third, then there is nothing wrong with it."
أَخْبَرَنَا أَحْمَدُ بْنُ خَالِدٍ، عَنْ مَعْنٍ، قَالَ حَدَّثَنَا مُعَاوِيَةُ بْنُ صَالِحٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، قَالَ إِذَا طُبِخَ الطِّلاَءُ عَلَى الثُّلُثِ فَلاَ بَأْسَ بِهِ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 5723
In-book reference : Book 51, Hadith 185
English translation : Vol. 6, Book 51, Hadith 5726