What is the ruling if I prayed the obligatory prayer but cannot recall the surahs I recited?

If you have prayed the obligatory prayer and recited Al-Fatihah in every Rakah, and what was easy from the Quran in the Rakahs in which it is sunnah to recite it along with Al-Fatihah, then your prayer is valid and in accordance with the Sunnah. Your inability to recall the Surahs you recited does not harm your prayer.

Humility and presence of heart are requested in prayer, which may help in recalling what was recited. However, the most important thing is to recite Al-Fatihah in every Rakah because it is a pillar, based on the Prophet's (peace be upon him) saying: "There is no prayer for one who does not recite the Mother of the Quran."