Bayan_CU at IslamicEval 2026: Fine-Grained Hallucination Span Detection in Arabic Quranic and Hadith Texts

Samah Ghonem


Abstract
Mitigating factual hallucinations in Large Language Model (LLM) responses is critical, especially when handling sacred Islamic text. This paper presents our system for the IslamicEval 2026 Shared Task-Subtask 1 (Span Detection), which requires extracting exact character-level spans and fragment labeling of religious citations in Arabic LLM-generated responses. We frame this as a supervised token-classification task, fine-tuning a monolingual bidirectional encoder (AraBERTv2). To process long sequences, we implement a sliding window chunking mechanism with an overlapping stride. We reconstruct final character boundaries using a post-processing heuristic that resolves overlapping token predictions. Furthermore, we apply a cascading false-positive filter using cross-type conflict resolution and category-specific minimum length thresholds. Our pipeline yields highly competitive results, achieving a Macro-F1 score of 0.9652 on the development set and a peak evaluation score of 0.9736 on the official-task test set.
Anthology ID:
2026.arabicnlp-sharedtasks.133
Volume:
Proceedings of The Fourth Arabic Natural Language Processing Conference: Shared Tasks
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Muhammad Abdul-Mageed, Tamer Elsayed, Houda Bouamor, Samhaa El-Beltagy, Hend Al-Khalifa, Ahmed Abdelali, AbdelRahim Elmadany, Abdellah El Mekki, Kareem Darwish, Sakhar Alkhereyf, Hamzah Luqman, Salam Khalifa, Samar Magdy, Zaid Alyafeai, Injy Hamed, Wajdi Zaghouani, Imed Zitouni
Venue:
ArabicNLP
SIG:
SIGARAB
Publisher:
Association for Computational Linguistics
Note:
Pages:
1081–1087
Language:
URL:
https://aclanthology.org/2026.arabicnlp-sharedtasks.133/
DOI:
Bibkey:
Cite (ACL):
Samah Ghonem. 2026. Bayan_CU at IslamicEval 2026: Fine-Grained Hallucination Span Detection in Arabic Quranic and Hadith Texts. In Proceedings of The Fourth Arabic Natural Language Processing Conference: Shared Tasks, pages 1081–1087, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Bayan_CU at IslamicEval 2026: Fine-Grained Hallucination Span Detection in Arabic Quranic and Hadith Texts (Ghonem, ArabicNLP 2026)
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PDF:
https://aclanthology.org/2026.arabicnlp-sharedtasks.133.pdf