´It was narrated that Ash-Sha'bi said:` "Ali, may Allah be pleased with him, used to give the people thickened grape juice into which flies would fall and not be able to get out again."
Hadith Referenceسنن نسائي / كتاب الأشربة / 5721
Hadith Gradingالألبانی:صحيح الإسناد موقوف | زبیر علی زئی:ضعيف، إسناده ضعيف، مغيرة بن مقسم عنعن. انوار الصحيفه، صفحه نمبر 368
(1) The intent here is that it (the drink) used to be very thick. The thicker it is, the more it will be protected from causing intoxication. Thus, the reason for prohibition is intoxication. Whatever contains intoxication, even if it is just a coating (ṭilāʼ), is forbidden.
(2) The aforementioned four narrations have been declared weak in their chains of transmission by the researcher of the book, but due to their mutual support and the presence of other corroborating evidences, they are considered valid as proof. Therefore, Shaykh al-Albani rahimahullah and other researchers have declared them authentic.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 5721