To what extent are the Hadiths valid concerning the virtue of fasting the first ten days of Dhu al-Hijjah, and is fasting these days a Sunnah?

It has been previously established that it is desirable to fast the first nine days of Dhul-Hijjah. As for the hadith, "There are no days in which worship is more beloved to Allah than the ten days of Dhul-Hijjah. Fasting each day of them is equivalent to fasting a year, and standing [in prayer] during each night of them is equivalent to standing [in prayer] during Laylat al-Qadr," its chain of narration is unanimously considered weak due to Al-Nahhas ibn Qahm and Mas'ud ibn Wasil.

As for the hadith, "There are five [things] that the Prophet, peace and blessings be upon him, never abandoned...", its chain of narration and text are shaky (mudtarib). It has been narrated in different versions from Hunaidah ibn Khalid: sometimes from the Mother of Believers Hafsah, sometimes from his wife from some of the wives of the Prophet, peace and blessings be upon him, sometimes from his mother from Umm Salamah, sometimes from his wife from Umm Salamah, and sometimes from the Mother of Believers without specifying her name. This has led to a difference of opinion among critics regarding its ruling, with most of them weakening it due to the shakiness of its chain of narration and text.