Is there a basis for custom in legislation?

The questioner : All right, a question on the principles of jurisprudence, Shaykh. In the principles, one of the disputed sources of legislation is custom. Some permit it, and some deny it. So could you elaborate on this issue for us?

The Shaykh : Custom, my brother, has no connection to the rulings of the Shari'ah. Rather, it has a connection to certain terms that some people rarely use, and they have a specific custom regarding them. An example of this is what is mentioned in the books of Islamic jurisprudence: if a person swears that he will not eat meat, does he break his oath if he eats fish? Fish, by the explicit text of the Noble Qur'an: I think this is the verse, so it is meat. But if it is the custom of a country that when a person says, "I bought meat" or "I ate meat," it never occurs to him that he might mean fish; it does not come to his mind that he means fish. In that case, if a person swears this oath and takes this vow, we say here that he must refer to the custom of his country. And I am now reversing the example for you: a person in some coastal countries who knows of meats only fish meat, as for sheep meat, camel meat, or goat meat, these do not occur to them because these animals do not live on their coast. So one of them says, "By Allah, I will not eat meat for such and such days." Then he travels, for example, to a country where these meats are known, and he eats some of them. Does he break his oath? We refer to the custom of his country: what does he mean by meat? He means fish. So in such a case, custom comes into play. As for changing rulings or altering rulings, Islam came with texts, some of which are detailed and some of which are general, encompassing many and very many particulars. We do not need to take rulings from the customs of people, especially since they differ completely, as I gave you an example earlier regarding the term "meat." This is not related to the rulings of obligation, but rather to things a person has obligated upon himself. In that case, it is said to him, "What do you mean?" From here came the scholars' and jurists' distinction between certain terms in the same country where they are spoken. For example, they made divorce into two categories: explicit divorce and implied divorce. If it is known in a certain country that when a man says to his wife, "Go to your family," and he means by this phrase divorce, it is as if he said to her, "I have divorced you." But if it is in another country where they do not mean this meaning, it does not enter into implied divorce at all, because this is not what is meant in the specific country I am referring to. So these terms are not for changing the rulings of the Shari'ah, but rather for clarifying personal intentions related to some of those who utter them.

The questioner : Those who permit it, Shaykh, cite the hadith of Hind that Abu Sufyan is a stingy man, so the Prophet (peace and blessings be upon him) said to her: So the "known" here, they expanded upon it a little.

The Shaykh : There is no objection. What is meant here by "known"?

The questioner : I mean what is the custom in that country regarding spending.

The Shaykh : In another country, the matter is different. This is not a restriction of a Shari'ah ruling, but rather customs differ from country to country, and it is never related to a fixed ruling in the Shari'ah. This hadith is authentic without a doubt.
Al-Halabi : Is it not said that the term "known" here has no connection to custom, but to "known" meaning without injustice, and without taking money excessively by right, and so on?

The Shaykh : It is possible to say this, in fact. "Known" is not "custom."