Answered by Shaykh Faraz Rabbani
What are the different opinions within the hanafi madhab on the permissibility or otherwise of praying behind an imam who follows a different madhab (i.e. one of the other three canonical madhahib)?

In the Name of Allah, the Beneficent, the Merciful, and all blessings and peace upon our master Muhammad, his Folk, Companions and those who follow their noble way,
The relied upon opinion is that it is valid to pray behind another imam as long as he fulfills the conditions & integrals (fards) of the Hanafi prayer. This would include wudu. This is inevitably true, as the Shafi`is have far many more fards than we do in tahara and prayer, and the default is that they would do their sunnas.
As for doing the Hanafi wajibs and sunnas, this cannot be accepted. In this, as Mulla Ali al-Qari and Ibn Abidin explain, each person follows what the ijtihad of their school indicates.
This would apply to the beard, too. In the Shafi`i school, it is NOT wajib for the beard to be a fistful, as mentioned in their relied upon texts, such as Imam al-Nawawi’s Minhaj and its commentaries, as mentioned by Shaykh Amjad Rasheed, the brilliant young Jordanian Shafi`i faqih and Shafi`i scholars in Damascus.
Wassaam,
Faraz Rabbani.