The One Who is led in Prayer should recite Al-Fatihah in all Circumstances

Question :

What is required of the one who is led in prayer when he prays? And should he recite with the Imam, or listen to the recitation of the Imam?

Answer:

The one who is led in prayer must recite Al-Fatihah in all circumstances, in the silent prayers and in the audible prayers. As for other than Al-Fatihah, in the audible prayers, he should be silent during the recitation of his Imam and it is not permissible for him to recite, according to the words of the Prophet to his Companions, may Allah be pleased with them, when he heard them reciting with him;
"Do not do so, except Umm Al-Qur'an (Al-Fatihah), because there is no prayer for one who does not recite it.

Also, the one who is led in prayer is different from the individual worshipper, because if the Imam says: "Sami“ Allāhu liman hamidah" (Allah hears the one who praises Him), the one who is led in prayer says: "Rabbana wa lakal-hamd" (Our Lord! All praise is due to Allah), because the Prophet said:

"The Imam is there to be followed, so if he says: "Allahu Akbar", then you say: "Allahu Akbar" and do not do so until he does. And if he bows, then you bow, and do not do so until he does. And if he says: "Sami' Allahu liman hamidah", then say: "Rabbana wa lakal-hamd". And if he prostrates, then you prostrate, and do not do so until he does. And if he prays standing, then you pray standing. And if he prays sitting, then all of you pray sitting.

Source:
Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 2 Pages 206-207