عَنْ أَبِى هُرَيْرَةَ عَنِ النَّبِىِّ -صلى الله عليه وسلم- قَالَ « إِذَا أُقِيمَتِ الصَّلاَةُ فَلاَ صَلاَةَ إِلاَّ الْمَكْتُوبَةُ
Abu Hurayrah (رضي الله عنه) narrated the Prophet (صلى الله عليه و سلم ) said” When the Iqamah is called there is no prayer except the obligatory prayer. “
Collected by Muslim (1673)Abu Dawud (1268) At-Tirmithi (421) An-Nisa’I (865) Ibn Majah (1151)
Benefits for this subject
- Five out of the six books of Hadeeth narrated this Hadith. Imam Al-Bukhari avoided it; as there was a difference about the status of the hadith being Marfu’  or Mawquf  .The hadith is saheeh and Marfu’
- Although Imam Al-Bukhari didn’t narrate this hadith he named a chapter in his Saheeh, “When the Iqamah is called there is no prayer except the obligatory prayer.” He used the hadith : Allah’s Messenger (ﷺ) passed by a man praying two rak`at after the Iqama (had been pronounced). When Allah’s Messenger (ﷺ) completed the prayer, the people gathered around him (the Prophet) or that man and Allah’s Messenger (ﷺ) said to him (protesting), Are there four rak`at in Fajr prayer? Are there four rak`at in Fajr prayer?” The title Imam Al-Bukhari wrote shows that his opinion was the congregational prayer invalidated the voluntary prayer at the call of the Iqamah. The words “Are there four rak`at in Fajr prayer? “confirm the Prophet (sallAllahu alayhi wa salam) disapproved of the man praying while the Iqamah was called. 
- This is 1 from the 20 ahadeeth that Imam Muslim narrated from Imam Ahmed ibn Hanbal through his chain in his Sahih.
- Abdur Rahman ibn Nasir As-Sa’dee (may Allah have mercy on him) said this hadith means that a person shouldn’t start a voluntary prayer at that time.
- This issue has four situations that can occur at the time of the Iqamah.
1: The Iqamah is called before the Muslim begins offering the voluntary prayer. In this situation he cannot begin with the Sunnah Prayer.
2: The Iqamah is called and there is no way possible that he can complete the Sunnah Prayer without missing one Rakah or the Tasleem altogether in the congregation. In this scenario it’s a must for him to stop the voluntary prayer in one opinion; as there is no contradiction between a Sunna and obligatory action. Starting the voluntary prayer doesn’t remove the obligation of the Jama’
3: If the Iqamah is called and it is possible for him to complete the Sunnah prayer and catch the first rakah, then in this case it’s better for him to complete the Sunnah. He should complete the Sunnah prayer moderately.
4: He has begun the prayer and the issue is between him completing the prayer and missing the first Rakah or discontinuing the prayer and catching the first Rakah. Generally speaking Sh Abdur Rahman viewed it was better to complete the Prayer offering it moderately, even if the first Rakah was missed. Furthermore, there is another view in the Hanbali law which says it is better to stop the prayer when the Iqamah is called based on the general meaning of the hadith and it’s permissible to cease a voluntary act.
- Shaykh Abdur Rahman As-Sa’di (May Allah have mercy on him) concluded with the opinion in number 3 above based on the verse. “and render not vain your deeds.” [ Surah Muhammad: Verse (33) ] 
- The researcher (Abu Aaliyah ) considers after looking at the four scenarios explained by his Shaykh Abdullah ibn Aqeel and Imam Al-Bukhari’s fiqh in the issue the position of Imam Al-Bukhari is the strongest. That is no prayer is offered at the time of the Iqamah, and if a person is praying he should discontinue that prayer without saying the Tasleem. An important note to add is scholars and Imams have differed over this issue and the situations described above from 1-4 give the slave of Allah a clear picture. Shaykh Al-Uthaymeen recommended number 3 above and said it made no difference if the Muslim was offering, Tahiyatul Masjid, the Ratib prayer or just praying voluntarily if he was in the 2nd Rakah he should complete it moderately.
Completing the prayer moderately in this case could be done by reading only Fatihah without a surah after it, and saying the legislated Tasbeeh once in Ruku and once in Sujud.  Allah knows best.
Abu Aaliyah Abdullah ibn Dwight Lamont Battle
 A hadeeth attributed to the Prophet
 A narration attributed to the companions
 Lubul Lubab fi At-Tarajim wal Abwab fee Sharah Abwab Sahih Al-Bukhari, by Al-Alamah Abdul Haqq Al-Hashami(1392 H), vo1/pg 380.
 Refer to The Fatwa of ibn Aqeel(Shaykh Al-Hanabala ) vol 1/page 292-293
 Fatawa nur ala Darb vol4/ 346-347 , by Al-Alama Muhammad ibn Salih Al-Uthaymeen
 Ibid refer to page 454