This is the day wherein the "neither born nor begotten" was born

 حضرت بهاء‌الله در يکى از الواح نازله به مناسبت يوم تولّد خودشان فرموده‌اند:

"فيه ولد من لم يلد و لم يولد" يعنى امروز روزى است که "لم يلد و لم يولد" در آن متولّد شد.

English Translation : 'in it is the one who is neither born nor begotten' [i.e. in reference to the 3rd verse of Quran 112]; meaning, today is the day wherein the "neither born nor begotten" was born therein.

The claim Baha'u'llah is attempting to make here, which falls flat on its face, is that he is the One Uniquely Single (الأحد) Who is the Everlasting (الصمد) that in high Islamic metaphysics is glossed as the completely unknowable and transcendent aspect of the ipseity of the Essence of the Godhead.