´'Abdur-Rahman bin Sa'd bin 'Ammar bin Sa'd, who was the Mu'adh-dhin of the Messenger of Allah narrated from his grandfather, that:` The Messenger of Allah commanded Bilal to put his fingers in his ears when calling the Adhan, and he said: "It makes the voice louder."
Related hadith on this topic
Explanation & Benefits
Maulana Ataullah Sajid
Benefit:
The chain of narration of this report is weak; however, the issue itself is correct, as is coming in the following hadith.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 710