What does one do if the iqamah is called while he is praying a voluntary prayer?

Question:
The questioner says: The iqamah was called for the Fajr prayer, and I had completed the first rak'ah of the sunnah, which is the preferred one. What is the ruling? Should I cut off the sunnah and join the obligatory prayer, or is it better to complete it?

Answer:
The Prophet (peace and blessings be upon him) said: Muslim recorded it in his Sahih. So, if the iqamah is called and you are in the rawatib prayer: the Fajr sunnah, or the Zuhr sunnah, or any other; you cut it off. This is what is prescribed, unless you are at the end of it, having performed the last bowing, so that nothing remains except a little. Then you complete it; because the minimum of the prayer is one rak'ah, and you have less than a rak'ah remaining, so you complete it and hasten to the obligatory prayer.
As for if the iqamah is called and you are in the first or second rak'ah before the bowing, you must cut it off by intention. You intend that you have exited from it, and you occupy yourself with preparing for the obligatory prayer; because the obligatory prayer is more important, and the voluntary prayer is made up afterwards. So, if the Fajr sunnah is missed, you pray it after Fajr, or after the sun rises, and praise be to Allah. And if the Zuhr sunnah before it is missed, you pray it afterwards.