✅ Answer: What has reached us from the narrations is that raisins (zabeeb) or grapes (kishmish) become problematic in two general cases, both of which are mentioned in the following narration:

زَيْدٌ النَّرْسِيُّ فِي أَصْلِهِ، قَالَ: سُئِلَ أَبُو عَبْدِ اللَّهِ عَنِ الزَّبِيبِ يُدَقُّ وَ [يُلْقَى] فِي الْقِدْرِ ثُمَّ يُصَبُّ عَلَيْهِ الْمَاءُ وَ يُوقَدُ تَحْتَهُ فَقَالَ لَا تَأْكُلْهُ حَتَّى يَذْهَبَ الثُّلُثَانِ وَ يَبْقَى الثُّلُثُ فَإِنَّ النَّارَ قَدْ أَصَابَتْهُ قُلْتُ فَالزَّبِيبُ كَمَا هُوَ [يُلْقَى] فِي الْقِدْرِ وَ يُصَبُّ عَلَيْهِ الْمَاءُ ثُمَّ يُطْبَخُ وَ يُصَفَّى عَنْهُ الْمَاءُ فَقَالَ كَذَلِكَ هُوَ سَوَاءً إِذَا أُدَّتِ الْحَلَاوَةُ إِلَى الْمَاءِ فَصَارَ حُلْواً بِمَنْزِلَةِ الْعَصِيرِ ثُمَّ نَشَّ مِنْ غَيْرِ أَنْ تُصِيبَهُ النَّارُ فَقَدْ حَرُمَ وَ كَذَلِكَ إِذَا أَصَابَتْهُ النَّارُ فَأَغْلَاهُ فَقَدْ فَسَدَ

📚 *Mustadrak al-Wasa'il*, Vol. 17, p. 38

Translation: Imam al-Sadiq (AS) was asked about raisins (kishmish) that are crushed and thrown into a pot, water is added, and fire is set underneath. Imam said: 'Do not eat it until two-thirds of the water evaporates and one-third remains because the fire has reached it.' The narrator said: 'I asked: What if the raisins (kishmish) are thrown into the pot as they are (without being cut) and water is added and it is cooked, and the water is then strained? What about this?' He replied: 'This is the same as the previous case. When the sweetness from the raisins (zabeeb) spreads into the water and it becomes like syrup (grape juice), and then it boils without being exposed to fire, it is certainly prohibited. Likewise, if it is exposed to fire and boiled, it is certainly spoiled.'

Explanation: Based on the above narration and others in this regard, cooking raisins in water until it begins to boil or leaving raisins in water until it naturally boils and churns, makes it impermissible to eat. It must be heated until two-thirds of the water evaporates to make it lawful. However, raisins placed inside the cake batter and baked in the cake oven are not covered by this narration, and no other narration prohibiting it has been found, so it is permissible.