ابن قدامة
A village in the Crusader era (1123 CE) named "Gemmail", has been identified with Jamma'in. It was referred to as "Jamma'il" in medieval Arabic sources. The village was home to the Bani Qudama clan, who moved to Damascus in 1156, during Crusader rule in Palestine. Their leader, and the "khatib" (Muslim preacher) of the village, Ahmad ibn Qudama (father of Ibn Qudamah and grandfather of Diya al-Din), left Jamma'in due to fears of persecution by King Baldwin, who intended to punish Ibn Qudamah for preaching against Crusader rule. The hilly and uninhabited area of Damascus the Banu Qudamah settled became the al-Salihiyah suburb, which was named either after the family, who were known as "the pious ones" ("as-salihiyyin") or after the Abi Salih Mosque, which the family was associated with. Throughout the 11th and 12th centuries, Jamma'in was a center for Hanbali activity. The medieval Syrian geographer Yaqut (1179–1229) described the site as "A well in the hill of Nabulus, in the Filastin Province. It lies a day's journey distant from Jerusalem, and belongs to that city." Diya al-Din (1173-1245) refers to the presence of Muslims in Jamma'in during his lifetime, and he also noted that the village had a mosque.