Samanid rule in Bukhara was not formally recognized by the caliph until the early 10th century when the Saffarid ruler 'Amr-i Laith had asked the caliph for the investiture of Transoxiana. The caliph, Al-Mu'tadid however sent the Samanid amir, Ismail Samani, a letter urging him to fight Amr-i Laith and the Saffarids whom the caliph considered usurpers. According to the letter, the caliph stated that he prayed for Ismail who the caliph considered as the rightful ruler of Khorasan. The letter had a profound effect on Ismail, as he was determined to oppose the Saffarids.