An Historical Atlas of Central Asia" written by Yuri Bregel. This is stated on Page no 23 of this book.

Although the greatest external expansion of the Samanid state took place under Isma#il b. Ahmad (892-907), it was during the reign of Nasr II b. Ahmad (914-943) that the state experienced its greatest prosperity. The capital of the state was Bukhara, which was the seat of the central administration modelled upon the caliphal court in Baghdad. The head of the Samanid family had the title of amir, lit.
“commander,” but meaning rather “governor” (for the caliph); the Samanids continued to nominally recognize the supreme authority of the caliph, but actually were completely independent. The amir appointed provincial governors, primarily from among the members of the Samanid family, but also from among other noble families
and later from among the Turkic slave soldiers. The governor had to collect taxes and supply troops for military campaigns, and for his service would retain for himself a certain share of the tax revenue from the province (sometimes all of it). In a number of provinces the Samanids retained the old dynasties as their vassals. While Khorezm was included in the Samanid state after 900, the local dynasty of the Khorezmshahs (in modern scholarly
literature, the Afrighids, from the name of its legendary ancestor), with their capital at Kath, continued to rule the southern part of the country, while the Samanid governor (amir) ruled the northern part, with the capital in Gurganj. In 995 the amir of Gurganj defeated the Khorezmshah and annexed his domain,
Assuming the title of Khorezmshah, but remained a Samanid vassal. Chaghaniyan was ruled by the Muhtajids (or Al-i Muhtaj), who were descendants of either the pre-Islamic rulers, the chaghan-khudas, or of an Iranized Arab family that had settled in Khorasan after the Arab conquest. Khuttal was ruled by a local dynasty known first as Banijurids and later (by the name of its other branch) Abu Davudids; the latter expanded their domain and included in it Balkh, Tokharistan and Termez. The province of Guzganan (in Arabicized form, Juzjan), southwest of Balkh, was ruled by the Farighunid dynasty. Kuhistan was the domain of the Simjurid family. Even the Saffarids remained for a while in Sistan as Samanid vassals.
In the west, Samanid vassals were the Zaydi Imams in the Caspian provinces. In the north, after the conquest of Isfijab, the Samanids left in place the local Turkic rulers. All these vassals sent only annual presents to the Samanid court, but paid no taxes. The largest province of the Samanid state was Khorasan, with its center in Nishapur, whose governor was also the commander-in-chief (sipahsalar) of the Samanid army. In the 940s and 950s Abu #Ali Chaghani (from the Al-i Muhtaj dynasty) was the governor of Khorasan and was close to establishing his independent rule there.
Later, it was the commanders of Turkic slave troops who held this governorship, often hardly recognizing central authority; in 991 such a commander, Abu #Ali Simjuri, appropriated all state revenues from Khorasan