diff --git a/src/prof.c b/src/prof.c
index 284b4c3..5dfe51e 100644
--- a/src/prof.c
+++ b/src/prof.c
@@ -1,3 +1,6 @@
+// Source: https://github.com/tsoding/wang-tiles/blob/0aebe3bb5d4ded4a163ed597b0cc7790177333e9/src/prof.c
+// Licensed under MIT. https://github.com/tsoding/wang-tiles/blob/0aebe3bb5d4ded4a163ed597b0cc7790177333e9/LICENSE
+
 // TODO: document how to use the profiler module @doc
 #include <assert.h>
 #include <time.h>