Musannaf Ibn Abi Shayba 33:1462

Ishaq ibn Mansur narrated to us, from Sulayman, from Abu Sinan, from Abdullah ibn Malik, who said: "Indeed, Allah has vessels on the earth; He does not accept from them except the firm, the tender, and the pure." He said: "The firm in the obedience of Allah, the tender at the remembrance of Allah, and the pure, free from filth."