In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
There is a difference of opinion among scholars and schools of jurisprudence on this issue. According to the Shafi`i school, the prayer of the followers is not invalidated by the invalidity of the prayer of the imam. According to the Hanafi school, the validity of followers’ prayer is dependent on the validity of imam’s prayer.
However, the middle position is if both were unaware of the fact at the time of prayer, then the invalidation of imam’s prayer does not affect the validity of the prayer of the followers. This is the preferred view of many scholars from diverse schools. It is also the view of many traditionists; it is more reasonable and stronger in light of the evidence of the sources as well as the precedents of the early Muslims.
Abu Hurairah reports that the Prophet (peace be upon him) said: “Your leaders will lead you in prayer. If they conduct it properly, you and they will be rewarded; but if they make mistakes you will earn the reward and they will be held responsible (for the mistakes).” (Al-Bukhari)
Imam Ibn Al-Mundhir says, ‘this hadith shows that the invalidation of the imam’s prayer does not affect the validity of the prayers of the followers.’
Having said this, I should point out: what we said above does not apply to cases where both parties knew that the imam’s prayer was wholly invalid. That would be the case if the imam knowingly omitted an essential condition or integral of the prayer: i.e. deliberately prayed without wudu, while the followers also knew about it; or he faced the wrong direction; or prayed without covering the awrah, or did not read the opening takbir, etc.
In light of the above, since the followers did not know that you had no wudu, their prayers are valid; and there is no need for them to repeat the Prayer; in your case, however, it is necessary to repeat the same.
Almighty Allah knows best.