Mukhtar was a good man. He fasted to thank Allah for His blessings. Allah granted him victory over the Prophet's enemies, who killed his grandson and robbed his family of their possessions. Mukhtar thought that Allah's blessings are countless. Concerning this, Allah the Glorified said:
And if you count Allah's favours, you will not be able to number them.
So, Mukhtar fasted for most days of the year.