Sunan Ibn Majah · Hadith 731
The Book of the Adhan and the Sunnah Regarding It - كتاب الأذان والسنة فيها
حدثنا هشام بن عمار، حدثنا عبد الرحمن بن سعد بن عمار بن سعد، مؤذن رسول الله صلى الله عليه وسلم حدثني أبي عن أبيه عن جده أن أذان بلال كان مثنى مثنى وإقامته مفردة .
'Abdur-Rahman bin Sa'd bin 'Ammar bin Sa'd narrated (from his great-grandfather of the Messenger of Allah) that: In the Adhan of Bilal, the phrases were two by two, and in his Iqamah they were said once.
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).