Is Nafil allowed after Faraz of Asr ?

I performed *Nafil* prayer(namaz) after *Asr Faraz* namaz, one person came and said you should not perform any namaz (Salah) after Asr Faraz. I would like to know is it allowed to offer *Nafil* namaz after Farz namaz of Asr? There is a same doubt with offering *Nafil* namaz after Fajr. Would anyone clarify on this?