It is therefore conceivable that, by the doorway and up on the roof, there stood a raised structure that looked very much like a minaret. Supporting evidence may be found in what Ibn Saʿd records in al-Ṭabaqāt 8/307, where—through his chain—he cites Umm Zayd ibn Thābit as saying:
“My house was the tallest of the houses surrounding the mosque, so Bilāl would deliver the adhān from its roof from the first time he ever called to prayer until the Messenger of Allah ﷺ built his mosque. Afterwards, he called from the roof of the mosque, and something had been erected for him above that roof.”
Its chain of transmission, however, is weak.
Abū Dāwūd and others also relate the report with a sound chain, but without the words: “and something had been erected for him above the roof.” And Allah knows best.
The conclusion I have reached on this matter is that no reliable evidence proves that a minaret inside the mosque was known during his ﷺ lifetime¹, even though it is certain that the adhān in those days was being given