Answered by Ustadh Tabraze Azam
Question: Assalam alaikum,
Is it true that the only way to make up missed obligatory prayers is by offering voluntary prayers?
Answer: Wa alaikum assalam wa rahmatullah,
What you have been told is incorrect. Missed prayers must be specifically made up, namely, by intending that you are making up the last missed Fajr prayer you owe, for instance. [see: What is the Proper Intention for Makeup Prayers?]
Please see: A Reader on Missed Prayers
And Allah Most High alone knows best.
Checked & Approved by Shaykh Faraz Rabbani