Getting /usr/src to match specific git hash?

[Steve Kargl]

Suppose one has an empty /usr/src.

Suppose further that one had to re-install a 32-bit
i386-*-freebsd with the 24 Dec 2020 image available
from freebsd.org.

uname -a for the booted kernel shows

% uname -a
FreeBSD mobile 13.0-CURRENT FreeBSD 13.0-CURRENT #0 \
3cc0c0d66a0-c255241(main)-dirty: Thu Dec 24 05:43:23 UTC 2020 \
root at releng1.nyi.freebsd.org:/usr/obj/usr/src/i386.i386/sys/GENERIC i386

How does one use git to pull the exact sources that match
this specifc kernel?

-- 
Steve