What is the ruling on saying: "By your preciousness, I want this," or "By the preciousness of so-and-so, do such-and-such"? Is it permissible to use such phrases?

If the utterance is intended as an oath, then it is impermissible to pronounce it, because swearing by other than Allah Almighty is forbidden, due to the Prophet's (peace and blessings be upon him) saying: "Whoever swears by other than Allah has disbelieved or associated partners with Him," and his saying: "Whoever is to swear, let him swear by Allah or remain silent."