´It was narrated that Jabir said:` "I entered the house of the Prophet with him and there was some bread and vinegar. The Messenger of Allah said: 'Eat; what a good condiment is vinegar.'"
Hadith Referenceسنن نسائي / كتاب الأيمان والنذور / 3827
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم
1؎ : Therefore, if someone who has sworn an oath not to eat curry (salan) eats vinegar, he will be considered as having broken his oath, and he will be required to offer expiation (kaffarah) for the oath.
Explanation & Benefits
Hafiz Muhammad Ameen
The term "salan" (curry/condiment) does not refer to any specific thing; rather, anything by which bread becomes moistened or passes easily down the throat—whether it is in the form of broth and liquid, or in a solid form such as meat, egg, etc.—will be called "salan." Vinegar also moistens the bread and, with the help of its flavor, assists in passing it down the throat, and in fact, aids in digestion as well. These are precisely the characteristics of "salan," therefore vinegar is also considered "salan." If someone swears an oath not to use "salan" and then uses vinegar, he will have to offer expiation (kaffarah) for his oath, because his oath has been broken.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3827