What is the ruling on swearing by other than Allaah?

Question 309: Is it true that swearing by other than Allaah, using abstract things, is not considered Shirk (associating others with Allaah in His Divinity or worship), whereas swearing by concrete things is that which is considered Shirk?

Answer: Swearing by anything or anyone other than Allaah is an act of minor Shirk (associating other partners with Allaah that is not tantamount to taking a Muslim out of Islaam); based on the Hadeeth reported by Imaam Ahmad, ‘Aboo Daawood and Al-Tirmidee that the Prophet (peace be upon him) said: Anyone who swears by other than Allaah has committed Kufr or Shirk. If a person aims at glorifying the thing sworn by in the same way that Allaah is glorified, this is considered major Shirk (associating others with Allaah in His Divinity or worship that takes the Muslim out of Islaam), whether the thing sworn by is concrete or abstract; all this is not permissible... read more here.