Sayyid Ahmad Husamaddin (ra) added such a note about Hazrat Mahdi's (as) birthplace in his Istihracname:

An individual [Hazrat Mahdi (as)] will come from the Muslims, and the honor of that individual will shed light like the rays of the Sun from THE HIGHEST PEAK OF THE CAUCASUS.

(Osman Yuksel Serdengecti, Mabedsiz Sehir [The City with No Temple], Serdengecti Publication: VI, p. 107)