Abu Ja'far Ahmad ibn Yusuf ibn Hud (Arabic: أبو جعفر أحمد بن يوسف بن هود), known by the regnal name al-Musta'in Billah (Arabic: المستعين بالله, lit. 'He who looks for help to God'), was the fourth member of the Banu Hud family to rule the Taifa of Zaragoza. He ruled from 1085 to 1110. He was the son of Yusuf al-Mu'taman ibn Hud.