A’la Hadrat Imam Ahmed Raza Khan Brailwi Rahmatullah Alaih, have written about this matter in his book ” Nahju’s Salamah fi Hukmi Taqbili’l Ibhamayni fi’l Iqamah.” I present here the answer according to the Shafi’i school. Taqbil al-unbulatayn is amongst the fada’il al a’mal due the fact that its legal basis is da’if hadith.
Al Hafidh al Daylami have reported, “Whenever he [Abu Bakr] heard the Mu’addhin say: “I bear witness that Muhammad is the Messenger of Allah”, he would repeat this [phrase as it is the Mandub of Adhan] and would kiss the tip of the index fingers [or thumbs] and wipe his eyes. The Prophet (may Allah’s peace and blessings be upon him!) said: whosoever does what my friend [i.e., Abu Bakr] did, my intercession will come down upon him.”