The teaching , that Hashem assists those who come to purify themselves is found 4 places in Shas :
Shabos 104a
Yuma 38b
Avoda Zora 55a
& Minachos 29b.
Who says it ?
By Reish Lokish.
Why him ?
Now may be a good time for a gem of Torah study.
www.GemsofTorah.com