Al-ʿAbbās ibn Saʿid al-Jawharī (Arabic: العباس بن سعيد الجوهري; c. 800 – c. 860), known as Al-Jawhari, was a geometer who worked at the House of Wisdom in Baghdad and for in a short time in Damascus, where he made astronomical observations. Born (and probably dying) in Baghdad, he was probably of Iranian origin.^{[1][page needed]} His most important work was his commentary on Euclid's Elements, which contained nearly 50 additional propositions and an attempted mathematical proof of the parallel postulate.^{[citation needed]}

Described as having superb knowledge of Greek, which was unusual for a Muslim scholar), Al-Jawhari is credited with a translation into Arabic of the Indian polymath Shanaq al-Hindi's Book of Poisons.^[2]