Is it permissible to begin the prayer immediately after the muezzin says "Allahu Akbar" and before the adhan is completed?

It is prescribed for whoever hears the muezzin to repeat what he says, except for "Hayya ‘ala as-Salah (definition) (hasten to prayer)" and "Hayya ‘ala al-Falah (hasten to salvation)," for which one should say: "La hawla wa la quwwata illa billah (there is no might or power except with Allah)." Then, one should invoke blessings upon the Prophet and ask Allah to grant him the Wasilah (a high station in Paradise), and then perform the supererogatory prayer followed by the obligatory prayer. If someone prays during the Adhan (definition), he has contravened the Sunnah (definition), and it is better for the bowing to occur after the muezzin finishes, because Satan flees upon hearing the Adhan. This applies to those who are inside the mosque. As for someone who enters the mosque, he may either wait for the Adhan to finish and respond to it, or begin praying immediately. Starting the prayer during the Adhan is better to be avoided, but if one does so, there is no sin upon him.