Assalaamu alaykum wa rahmatullaahi wa barakaatahu Shaykh.
Is this hadith authentic?
Imam Ad-Darimi wrote:
Sa’eed Ibn Al-Musayyib said, “In the days of Harrah (when Yazeed attacked Madina.) For three days, there was no azan or iqamah (second, small call to prayer) in the mosque of the Prophet, sallallaahu 'alayhi wa sallam, I was in the Mosque by myself. From the grave of our Prophet, sallallaahu 'alayhi wa sallam, I heard the azan, and that is how I knew the time of the prayer.” [Darimi Chapter Fadhail Sayedul-Mursalin by Imam Darimi]

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

This hadeeth was classified as weak by Shaykh al-Albaani while classifying the ahaadeeth of Mishkaat al-Masaabeeh.

Allaah knows best.