The answer
Holy Book of Ps 139:15-16“My frame was not hidden from thee, when I was being made in secret, intricately wrought in the depths of the earth. Thy eyes beheld my unformed substance; in thy book were written, every one of them, the days that were formed for me, when as yet there was none of them.” (RSV)
The closest to the Arabic translation is the English translation of the Septuagint "My bones which thou madest in secret were not hidden from thee, nor my substance, in the lowest parts of the earth. Thine eyes saw my unwrought substance and all shall be written in thy book; they shall be formed by day though there should for a time be no one among them.”
The word 'frame' or in other translations 'substance' in Hebrew is 'Aatsmiy' which means, my bones or skeleton.
The depth of the earth symbolizes the mother's womb.
V. 16 means God knew us before we were composed of either flesh or bone (unformed substance), our .members (every one of them) were written in His book, and the days that (our members) were formed for us, even as yet there was none of them (members).
Answered by His Eminence Metropolitan Youssef (opens in a new tab)