How sound is the Hadith that states that whoever speaks during the Adhan will not be able to utter the Shahadatayn at the time of death?

It is permissible to speak during the Athan (call to prayer). The Companions of the Prophet used to converse during the Friday Athan in the era of Umar ibn al-Khattab, may Allah be pleased with him. The Prophet, peace and blessings be upon him, heard a man speaking during the Athan and did not object to him. As for the Mu'adhdhin (the one who calls the Athan) himself, scholars have differed regarding the ruling on his speaking. However, if his speech is prolonged and the continuity between the words of the Athan is broken, the Athan becomes invalid and must be repeated.