the Bab employed the title Subh-i-Azal in reference to various other leading Babis

This title of honour [Subh-i-Azal] was evidently not conferred on him by the Bab, who only called him Thamaratu’l-Azaliyya and Ismu'l-Azal (see Mirza Yahya, Mustayqiz, pp. 391f). However, the Bab did employ the title Subh-i-Azal in reference to various other leading Babis (see the commentary on the Hadith of Kumayl, Teheran Baha'i Archives MS 6006C, pp. 74ff.)

(Making The Crooked Straight by Udo Schaefer, Nicola Towfigh, Ulrich Gollmer, p. 631)