Allah may swear by whatever of His creatures He wills, but His creatures are not permitted to swear by anything other than Allah. Many people swear all kinds of oaths by things other than Allah, but swearing by something is like glorifying it, and it is not right to glorify anything or anyone other than Allah. Ibn ‘Umar reported that the Prophet (peace and blessings of Allah be upon him) said: “Allah has prohibited that you should swear by your fathers. If anyone swears, let him swear by Allah, or else remain silent.” (Reported by al-Bukhaari; see al-Fath, 11/530). Ibn ‘Umar also reported that the Prophet (peace and blessings of Allah be upon him) said: “Whoever swears by something other than Allaah is guilty of shirk.” (Reported by Imaam Ahmad, 2/125; see Saheeh al-Jaami’, 6204). The Prophet (peace and blessings of Allah be upon him) said: “Whoever swears by trustworthiness is not one of us.” (Reported by Abu Dawud 3253; see also al-Silsilah al-Saheehah, no. 94).
It is not permitted to swear by the Ka’bah, by trustworthiness, by honor, by help, by the blessing of so-and-so, by the life of so-and-so, by the virtue of the Prophet, by the virtue of a wali, by one’s father and mother, by the heads of one’s children, etc. All of that is haraam, and the expiation for doing it is to say La ilaaha ill-Allah, as is stated in the saheeh hadeeth: “Whoever swears and says ‘By al-Laat’ or ‘By al-’Uzza,’ let him say ‘La ilaaha ill-Allah (there is no god except Allah).’” (Reported by al-Bukhaari, al-Fath, 11/536). There are other phrases that similarly involve shirk and are therefore forbidden, but that are often spoken by Muslims, such as: “I seek refuge with Allah and with you,” “I am depending on Allah and on you,” “This is from Allah and from you,” “I have no-one but Allah and you,” “I have Allah in heaven and I have you on earth,” “If it were not for Allah and so-and-so,” “I disown Islam,” “Time has let me down” (and every other expression which involves cursing time, like saying, “This is a bad time,” “This is an unlucky time,” “Time is a betrayer,” etc., because cursing time is an insult to Allah Who has created time), references to “Nature’s way.” Names that imply being a slave of anyone other than Allah, such as ‘Abd ‘al-Maseeh, ‘Abd al-Nabi, ‘Abd al-Rasool and ‘Abd al-Husayn, are also forbidden.
There are also modern expressions which are contrary to Tawheed and are therefore haraam, such as “Islamic socialism,” “Islamic democracy,” “The will of the people is the will of Allah,” “Religion is for Allah and the land is for the people,” “In the name of Arabism,” “In the name of the revolution,” etc.
It is also haram to use titles such as “King of kings” or “Judge of judges” for human beings; to address munafiqeen or kuffaar with titles like “Sayyid (master)” (whether speaking Arabic or other languages), to use the words “If only...” - which imply discontent and regret, and open the way for Shaytaan, and to say “O Allah, forgive me if You want to.” (For more information, see Mu’jam al-Manahi al-Lafziyyah, Bakr or Zayd)