Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.106.

The azhan is a form of worship. Muslims are not allowed to add or subtract anything from it. There is an authentic hadith which states, “Whoever introduces something to this affair of ours will have it rejected.” We will discuss some of these acts here:

The caller saying, “I bear witness that our leader (Muhammad) is the Messenger of Allah.” Ibn Hajr is of the opinion that the word ‘leader’ may not be added, although it is permissible on other occasions.

Shaikh Isma’il al-‘Ajluni records in Kashfal-Khafa’, “Wiping the eyes with the index fingers and then kissing them after hearing the caller say ‘I bear witness that Muhammad is the messenger of Allah,’ and with the listener saying, ‘I bear witness that Muhammad is His slave and messenger. I am pleased with Allah as Lord, with Islam as religion, and with Muhammad as the Prophet,” is based on ad-Dailami’s report from Abu Bakr that when he heard the caller say, “I bear witness that Muhammad is the Messenger of Allah,” he would say the same, kiss the inside of his index fingers and wipe his eyes. The Prophet then said, “Whoever does what my friend (Abu Bakr) did, then my intercession will be permissible for him.” In al-Maqasid it says, “This is not true. And what Abu Bakr ar-Raddad al-Yamani al-Mutasawaf recorded in Mujibat ar-Rahmah wa Aza’im al-Maghfirah is not true. Its chain is of unknown narrators and, moreover, the chain is broken.” There is another report of equally dubious import from al-Khidrs and mentioned in the preceding book: “Whoever says, upon hearing the caller say, ‘I bear witness that Muhammad is the Messenger of Allah,’ ‘Welcome O my love and the coolness of my eyes, Muhammad ibn ‘Abdullah, upon whom be peace,’ and then kisses his index fingers and wipes his eye with them, he well never go blind; nor will he never be afflicted with an eye infection.”‘ None of these practices can be attributed to the Prophet or his companions.