Q: I joined a jamaat salaah thinking it was zohr as hanafi asr had not started. Upon completion I found out it was in fact an asr jamaat as the time for asr for Shafi etc had begun. Was it obligatory for me to read the salaah again?
A: You had the intention of Zohar and they were performing Asr, so you will have to repeat your Zohar Salaah and perform Asr when the Hanafi time has entered.
Moulana Yusuf Laher