There is no difference in prayer between the recommended practice and the obligatory prayer in that reciting a surah after al-Fatihah is a recommended practice.

The questioner : Naturally, it is well known... the regular recommended practice regarding reciting al-Fatihah is that it suffices if you recite it... which is, of course, like standing and other things; of course, you recite whatever is easy for you after al-Fatihah. Now, if you recite in the regular recommended practice, O Shaykh, is there anything required of you?

The Shaykh : If you recite what?

The questioner : If you recite the regular recommended surahs after al-Fatihah?

The Shaykh : There is no difference; they call it "regular" meaning close, there is no difference... in distinguishing.

The questioner : ... I meant distinguishing.

The Shaykh : The sunnahs are the regular ones, and the regular ones are prayed like the obligatory prayers, and the obligatory prayers... the pillar in them is reciting al-Fatihah. Reciting a surah after al-Fatihah is a recommended practice. Now, if one does not recite in the obligatory prayer, his prayer is valid; consequently, if he does not recite in the regular ones and the sunnahs, his prayer is valid. But if he recites, it is better, just like in the obligatory prayer.

The questioner : If one prays voluntarily, for example, and recites al-Fatihah and then recites whatever is easy for him, and if he does the same thing in the regular sunnahs, is there no difference? May Allah reward you with good.

The Shaykh : And beware of that.