How many verses of Quran should be recited after al Fatihah in Jammah prayer?

I currently have another Muslim brother staying in my house. We have been praying some of our Salat together at home; sometimes he leads and sometimes I do. Sometimes when he leads Maghrib or Ishaa, he recites Ayah al Kursi (and no other Ayat) after the initial al Fatihah, then continues with Rukoo. I have always believed that the recitation after al Fatihah, in the first two Rakat, had to be at least three Ayat for the Salah to be valid. Am I wrong about this? So, is his Salah valid in this case? And is my Salah valid, when I am praying behind him? I don't want to correct him without being very sure about it. It's worth mentioning that my friend and I are both Sunnis.