It is permissible
to use vinegar as a condiment. It is narrated in
Sahih (authentic) Book of Hadith by Muslim
on the authority of
`Aishah (may Allah be pleased with her) that the Prophet (peace be upon him) said,
"The best food is (Part No. 22; Page No. 125) vinegar."
It is also related in Sahih Muslim on the authority of
Jabir ibn `Abdullah (may Allah be pleased with them both) that
"The Prophet (peace be upon him) asked his family for food. They (the members of his household) said, 'We have nothing but vinegar.' He asked for it, began to eat, and then he said, 'Vinegar is the best condiment, vinegar is the best condiment.'"
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.