In his 101 BE  Naw-Rúz message to the Baháʼís of the East (also known as the Lawḥ-i-Qarn, or “Tablet of the Centennial”), Shoghi Effendi included a prayer he composed, which is addressed to the Báb and reads like an apostrophe to him. What follows is my provisional translation (in other words, not official or authorized; see here for more) of this prayer. The original Arabic text of this prayer can be found in Tawqíʻát-i-Mubárakih: Khiṭáb bih Aḥibbáy-i-Sharq, pp. 270–271. The prayer has since been reprinted in several Persian and Arabic Baháʼí prayer books.
He is God
O Thou our Lord, the Most High! We beseech Thee, by Thy blood that was shed upon the earth, to answer our prayers, to shield us with the protection of Thy safekeeping, and to make the clouds of Thy generosity and beneficence to rain down upon us. We entreat Thee, moreover, to aid and confirm us in treading Thy path, in clinging to the cord of Thy love, in establishing Thy proof, in spreading abroad Thy signs, in repelling the wickedness of Thine enemies, in comporting ourselves with Thy virtues, and in proclaiming the Cause of Thy Beloved, the Most Glorious [Baháʼuʼlláh], in Whose path Thou didst offer up Thy life, desiring naught else but martyrdom in Thy love for Him.
Help us, O Lord our Beloved, the Most High! Strengthen our loins, make firm our steps, forgive our sins, and pardon our transgressions. Unloose our tongues that we may sing Thy praise and celebrate Thine attributes. Crown our deeds and endeavors with the diadem of Thine acceptance and good-pleasure. Grant that our own end may be even as the one Thou didst ordain for such among Thy servants as are devoted unto Thee, and draw us towards the shelter of Thy mercy. Cause us to enter into the realm of Thy luminous presence, and gather us together with such among Thy loved ones as are nigh unto God. Grant that we may step into Thy presence, and inebriate us with the wine of reunion with Thee. Suffer us to abide forevermore in the gardens of Thy holiness, and nourish us with every good thing that Thou hast ordained in Thy kingdom, O Succorer of the worlds.
A typed version of the complete Arabic text of this prayer appears below (vocalization mine).