Double entendre refers to when a person means something other than the apparent meaning of the words. It is permissible subject to two conditions:
1 – that the word may be interpreted in that fashion
2 – that there be no wrongdoing involved.
If a man says, “I only sleep on a watd” – a watd is a piece of wood placed on the wall for things to be hung from (i.e., a hook), but the man says that what he meant by watd was a mountain, this is an acceptable kind of double entendre, because the word watd may also mean a mountain, and there is no wrong being done to anyone in this case.
Similarly if a man says, “I only sleep under the saqaf (lit. roof),” then he sleeps on the roof, and says that what he meant by saqaf was the sky, this is also acceptable, because the sky is called saqaf in the verse where Allah says (interpretation of the meaning):
“And We have made the heaven a roof [saqafan], safe and well-guarded” [21:32]
But if you use double entendres in order to wrong someone, that is not permitted, such as if a person deprives another of something that is his due, then he goes to the qaadi (judge), but the one who was wronged has no proof, so the qaadi asks the one who took away his right to swear that he does not have anything that belongs to the claimant, and he swears saying, “Wallaahi maa lahu ‘indi shay’,” and the qaadi rules in his favour, then some of the people speak to him and told him that his oath was a false oath (yameen ghamoos) which may doom him to Hell. It says in the hadeeth, “Whoever swears an oath when asked to do so in order to deprive a Muslim man of his rights unlawfully, will meet Allah when He is angry with him.” The person who swore this oath said, “I did not mean to deny, I meant to affirm, and what I meant by saying “maa lahu” was “Of Whose I have something.” [i.e., I have something that belongs to Allah – because all things belong to Allah]. Even though what he said may mean this, his intention was to wrong another and not give him his due, so it is not permissible. Hence it says in the hadeeth: “Your oath is according to what your companion believes.” Twisting the meaning will not avail you anything before Allah, and you are now swearing a false oath.
If a man accuses his wife of betraying him and she is innocent of that and he swears an oath and says, “By Allah she is my sister,” and says that he meant she is his sister in Islam, then this is a valid statement, because she is his sister in Islam and she has been falsely accused.
Majmoo’ Duroos wa Fataawa al-Haram al-Makki by Shaykh Ibn ‘Uthaymeen.