He did not believe in the prognostication of the astrologer
When Ali led his troops against the Kharijites at the Battle of Nahrawan, an astrologer advised him not to proceed to battle as the time was not propitious. Ali refused to act on the advice saying: "All knowledge of the unknown belongs to God. I cannot accept any person as a partner in the knowledge of God."
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"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari