Is oral sex between married couples allowed according to Shia teachings? If so, what is the evidence for it from the teachings of the Prophet (s) and the Imams (s)?
Bismaillah,
Asalamu Alaykom,
It is permitted but if a woman was doing any particular act on her husband, then it is haram for her to consume any najasa.
Please read the following link which includes some ahadith and information on this matter:
https://www.al-islam.org/islamic-marriage-handbook-syed-athar-husayn-sh-rizvi/sexual-techniques
May Allah grant you success