Prayer: What if someone recites only Surah Fīl or Inshirāh alone in prayer without knowing they should be combined?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: What if someone recites only Surah Fīl or Inshirāh alone in prayer without knowing they should be combined?

English:

Question #467:

According to the opinion of some commentators of the Qur’an a number of its chapters, such as “Fīl” and “Quraysh”, and “Inshirāḥ” and “Ḍuḥā”, are not considered complete chapters. They believe that whoever reads the chapter “Fīl,” he should certainly read the chapter “Quraysh,” and the same rule applies to chapters “Inshirāḥ” and “Ḍuḥā” that should be read together. If someone reads the “Fīl” or “Inshirāḥ” chapter alone in prayer and does not know this rule, what will his duty be?

Answer #467:

The previous prayers are correct if he was not negligent in learning the rule.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer