In the name of Allah, the Most Merciful, the Most Compassionate
Hunaydah ibn Khaalid narrated upon the authority of his wife who said, “Some of the wives of the Prophet (salallaahu ‘alaihiwasallam) told me that the Prophet (salallaahu ‘alaihiwasallam) used to fast the Day of ‘Aashoorah, the first nine days of Dhul-Hijjah, and three days out of every month*.” (Imam Ahmad, An-Nasaaee)
Imam An-Nawwawee (rahimahullaah) said with reference to fasting the first nine days of Dhul-Hijjah: “It is extremely preferable to do so.”
Fatwah from Shaikh al-’Uthaimeen about fasting first Nine Days of Dhul-Hijjah, A questioner asked Shaikh al-’Uthaimeen (rahimahullaah) the following question:
Question: Oh Shaikh, are there any authentic ahadith that mention fasting the first [nine] days of Dhul-Hijjah?