The problem for many believers, of course, is that the con-
clusions of evolution appear to contradict certain sacred texts
that describe God's role in the creation of the universe, the
earth, all living things, and ourselves. In Islam, for instance, the
Qur'an describes life developing in stages, but sees humans as
a special act of creation "from sounding clay, from mud molded
into shape" (15:26). In Judaism and Christianity, the great cre-
ation story of Genesis 1 and 2 is a solid bedrock for many be-
I found this: Islam Question and Answer - So let man see from what he is created and this: sounding - WordReference.com Dictionary of English (2nd definition: Archaic).
So my guess is that "sounding clay" is a dry one that, when hit or struck, makes a sound.
Please be aware that I'm neither a native English speaker nor a teacher.