It is narrated that Imam Mahdi Ahs has said "When you buy an earthen pot for a paisa or two, you test it by knocking it repeatedly, and you buy it if it gives good sound and if it is not broken, cracked or damaged: otherwise, you return it; when you claim to be seeking Allah, how can you be let off without tests and trials?"
(Insaaf Nama - Matan Sharif, N.23)