Prayer: Is a traveler required to shorten all obligatory prayers or only specific ones?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: Is a traveler required to shorten all obligatory prayers or only specific ones?

English:

Question #637:

Does the obligation of saying shortened prayer by a traveler apply to all obligatory prayers or is it limited to some of them?

Answer #637:

The obligation of shortened specifically applies to some daily prayers, i.e., noon, afternoon and ‘ishā’. As for the morning and the maghrib ones, this rule does not apply.

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