Adhaan being Called out while Performing Tahajjud

Q: Salaah-67: I have a fervour for performing Tahajjud salaah. However, as I was performing two Rakaahs Tahajjud salaah one morning, the Fajr Adhaan was called out. After performing the two Rakaahs, I made enquiries and found out the Adhaan was called out on time, meaning that my two Rakaahs were performed after dawn (Subh Saadiq). Thinking about whether or not to perform the two Rakaahs Sunnah of Fajr, the Jamaa'ah stood up and I joined it without performing the two Rakaahs Sunnah of Fajr. What am I to do now? Is there Qadhaa for the Sunnah salaah?

Answer: If you are certain that the two Rakaahs wereperformed after dawn, they will replace the Sunnah Rakaahs of Fajr and it will therefore not be necessary to repeat the Sunnah.l And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2