His reign continued until the Franks seized Tripoli in the Maghrib by force in the year 541 AH. On that occasion al-Ḥasan fled from al-Mahdiyya⦗1⦘ with most of its inhabitants and later attached himself to Sultan ʿAbd al-Muʾmin.
On another occasion three strangers presented themselves to Yaḥyā, claiming they could practise alchemy. He had them brought in for entertainment and cleared the room for them, while his army commander Ibrāhīm and the noble Abū al-Ḥasan remained at his side. One of the three drew a knife and struck at the king, but accomplished nothing; the king kicked him away, sending him rolling, then entered an inner chamber and locked the door. The second assassin killed Abū al-Ḥasan. Ibrāhīm thereupon charged them with his sword, the mamluks burst in, and together they slew all three. The attackers proved to be Bāṭinīs; I suspect the Fāṭimid ruler al-Āmir had dispatched them for that purpose.
239 – Al-Darzijānī, Abū al-Faḍl Jaʿfar ibn al-Ḥasan
The Imām, Shaykh al-Islām, Abū al-Faḍl Jaʿfar ibn al-Ḥasan: a Hanbalī jurist, Qurʾān-reciter, and associate of Judge Abū Yaʿlā.
People transmitted hadith from him and from Abū ʿAlī ibn al-Bannāʾ. He taught a great many students, spoke the truth, enjoined what is right, enjoyed high standing, and commanded imposing respect.
Ibn al-Najjār praised him effusively, noting that he completed a full recitation of the Qurʾān every day in a single rakʿah, and that he had studied law under Abū Yaʿlā.