ومن كلام له (عليه السلام) لبعض أصحابه لمّا عزم على المسير إِلى الخوارج، فقال له: يا أميرالمؤمنين إن سرت في هذا الوقت، خشيتُ ألاَّ تظفر بمرادك، من طريق علم النجوم، فقال (عليه السلام):
When  Amīr al-mu’minin decided to set out for the battle with the Khārijites someone said, “If you set out at this moment then according to astrology I fear you will not be successful in your aim,” whereupon Amīr al-mu’minin said:
Do you think you can tell the hour when a man goes out and no evil befall him or can warn of the time at which if one goes out harm will accrue? Whoever testifies to this falsifies the Qur’ān and becomes unmindful of Allāh in achieving his desired objective and in warding off the undesirable. You cherish saying this so that he who acts on what you say should praise you rather than Allāh because according to your misconception you have guided him about the hour in which he would secure benefit and avoid harm.
ثم أقبل (عليه السلام) على الناس فقال : أَيُّهَا النَّاسُ، إِيَّاكُمْ وَتَعَلُّمَ النُّجُومِ، إِلاَّ مَا يُهْتَدَى بِهِ في بَرٍّ أَوْ بَحْر، فَإِنَّهَا تَدْعُو إِلَى الْكَهَانَةِ، والمُنَجَّمُ كَالْكَاهِنِ، وَالْكَاهِنُ كَالسَّاحِرِ، وَالسَّاحِرُ كَالْكَافِرِ! وَالْكَافِرُ في النَّارِ! سِيرُوا عَلَى اسْمِ اللهِ.
Then Amīr al-mu’minin advanced towards the people and said: O people ! Beware of learning the science of stars except that with which guidance is sought on land or sea, because it leads to divining and an astrologer is a diviner, while the diviner is like the sorcerer, the sorcerer is like the unbeliever and the unbeliever would be in Hell. Get forward in the name of Allāh.
 When Amīr al-mu’minīn decided to march towards Nahrawan to suppress the risings of the Khārijites, ‘Afīf ibn Qays al-Kindī said to him, “This hour is not good. If you set out at this time, then instead of victory and success you will face defeat.” But Amīr al-mu’minīn paid no heed to his view and ordered the army to march that very moment. In the result the Khārijites suffered such a clear defeat that out of their nine thousand combatants only nine individuals saved their lives by running away while the rest were killed.
Amīr al-mu’minīn has argued about astrology being wrong or incorrect in three ways, firstly, that if the view of an astrologer is accepted as correct it would mean falsification of the Qur’ān, because an astrologer claims to ascertain hidden things of the future by seeing the stars while the Qur’ān says: “Say: None (either) in the heavens or in the earth knoweth the unseen save Allāh . . .” (27:65)
Secondly, that under his misconception the astrologer believes that he can know his benefit or harm through knowing the future. In that case he would be regardless of turning to Allāh and seeking His help, while this indifference towards Allāh and selfreliance is a sort of heresy and atheism, which puts an end to his hope in Allāh.
Thirdly, that if he succeeds in any objective, he would regard of this success to be the result of his knowledge of astrology, as a result of which he would praise himself rather than Allāh, and will expect that whomever he guides in this manner he too should be grateful to him rather than to Allāh.
These points do not apply to astrology to the extent it may be believed that the astrological findings are in the nature of effect of medicines which are subject to alteration at will of Allāh. The competence achieved by most of our religious scholars in astrology is correct on this very ground that they did not regard its findings as final.