Fatwa ID: 05013
Answered by: Maulana Shadman Ahmed
If the Zuhr Fardh Salaah Jamaat had commenced: –
أ. Should the Musalli commence his four Sunnah Muakkadah or should he join the Imaam?
ب. If the Musalli has already commenced his four Sunnah before Jamaat started, then what should the Musalli do? Should he abandon the Sunnah or complete it?
ج. If the Musalli terminates the Sunnah by making Salaam after two Rak’aats in the first Qa’dah then will it be necessary for him to (repeat) make the Qadha of these Sunnahs especially since seeing that his Niyyah was for four Rak’aats and he only completed two?
In the name of Allah, the Most Gracious, the Most Merciful
If the Musalli feels that he will miss a rakat of the fard prayer, then he will not commence his four Sunnah Muakkadah. He should join the Jamat and make up the Sunnah after the Fard prayer before the two rakats sunnah. If the Musalli has commenced his four Sunnah before Jamat started, then the Fardh salah Jamat starts then he should pray only two rakats and say salam. He will make qada of four rakats as that is the intention, he started the prayer with. 
Only Allah knows best
Written by Maulana Shadman Ahmed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Ibn Abideen, Radd al-Muhtar, vol. 2, pg. 54; Fatawa Darul Uloom Deoband,vol. 4, pg. 159