"The Hammer of God" is a short story by G. K. Chesterton. It features his detective, Father Brown, and was published in the short story collection The Innocence of Father Brown (1911).
The brother of the vicar of the village where Father Brown has his parish church is a cad and a wastrel. When he's found near the church tower with his head smashed by a very small hammer, the local blacksmith is the first suspect, but it's his wife who confesses the murder!