Sadd al-Dharai (Blocking the means): Dharai (means) is the plural of Dhariah which signify means. Sadd means 'to block'. In Usul, it means 'blocking the means to evil'. Sadd al-Dharai is often used when a lawful means is expected to produce an unlawful result.
The concept of Sadd al-Dharai is founded on the idea of prevention of evil before it materializes. There are examples of Sadd al-Dharai in the Quran (for instance, 6:108 and 2:104). The 'means' must conform to the 'ends' (objectives of Shariah) and 'ends' must prevail over the 'means'. If the 'means' violate the purpose of Shariah, these must be blocked. The purpose (Maqasid) of Shariah are identifiable from the texts.
A general principle has been adopted by jurists that 'preventing harm takes priority over securing a benefit'. As such means, if they lead to evil, these must be rejected. Authority for Sadd al-Darai is also found in Sunnah. Prophet (SM) forbade a creditor to take a gift from debtor (as it could lead to taking of interest). He (SM) also forbade killing of hypocrites (as it could lead to dissention within community, also lead to wrongful killing on suspicion).
Despite the aforesaid, the Ulama of Usul are not in agreement over Sadd al-Dharai. Some accept it, some do not accept it. However, Shatibi is of the opinion that most Ulama have accepted it in principle, they differ only in application. Abu Zahra is also of the same opinion. (see textbook).
Dharai have been divided into the following four types from the point of view of their probability of leading to evil ends :
a. Means which definitely lead to evil. Such means are totally forbidden.
b. Means which most likely to lead to evil and rarely leads to benefit. Examples of this are selling weapons during war time and selling grapes to a wine-maker. Most Ulama have invalidated such means.
c. Means which frequently lead to evil, but there is no certainty or even dominant probability. Ulama differ widely on the illegality of such means (see text book).
d. Means which rarely lead to evil. Examples are digging well in a place which is not likely to cause harm or speaking a word of truth to a tyrannical ruler. Ulama have ruled in favour of permissibility of these means.
Sadd al-Dharai should not be used too much, particularly in the 3rd category stated above. Such use would render the 'mubah' (lawful) and the 'mandub' (recommended) as unlawful, which can not be accepted.
Ibnul Arabi and Abu Zahra are in favour of moderation in its use. People of extremist tendencies can use sadd al-dharai to restrict human freedom granted by Allah and the Prophet (SM) which must not be allowed to happen.(from Shah Abdul Hannan's "Usul al-Fiqh")