Shahada spread on both sides, with "al-Khalifa al-Mahdi" in the fourth line of obverse, date and mint in margins. Minted in 166 AH = 783 AD, mint of Medinat al-Salam. 24mm, 2.88 grams. Mitchiner WIS 159v; Lavoiux #733; S. 215.1.
This is a beautiful high quality coin showing original luster. It was reportedly found in Spain in a large hoard of Abbasid coins and Spanish Umayyad coins.
Muhammad ibn Mansur al-Mahdi (ruled 775-785), was the third Abbasid Caliph. He succeeded his father, al-Mansur. Al-Mahdi, whose name means "Rightly-guided" or "Redeemer", was proclaimed caliph when his father was on his deathbed.