The Quran

وَالَّذينَ استَجابوا لِرَبِّهِم وَأَقامُوا الصَّلاةَ وَأَمرُهُم شورىٰ بَينَهُم وَمِمّا رَزَقناهُم يُنفِقونَ

Ali Unal

And those who answer the call of their Lord and obey Him (in His orders and prohibitions), and establish the Prayer in conformity with its conditions; and whose affairs are by consultation among themselves;¹ and who spend out of what We provide for them (to provide sustenance for the needy, and in God’s cause);

Consultation is the first requirement for reaching the right decision. Decisions reached without due reflection or proper consultation usually come to nothing. Individuals who depend only on themselves are disconnected from others and unconcerned with the opinions of others; such people, even if they happen to be geniuses, are at considerable risk of error, as compared to those who exchange opinions and arguments (See Pearls of Wisdom, 77–78).
The advisory system is so important in Islam that God praises the first, exemplary Muslim community as a community whose affairs were conducted through consultation. This becomes even clearer when we realize that this first community was led by the Prophet, upon him be peace and blessings, who never spoke out of caprice or on his own accord, but only spoke about what was revealed to him by God (53: 2–3); God considers consultation so important that He ordered His Messenger, upon him be peace and blessings, to practice it with his Companions (3: 159). Even after the Muslims’ reverse at the Battle of Uhud (in 625), due to some of the Companions’ disobedience of the Prophet’s orders, God told him to engage in consultation. The Prophet, upon him be peace and blessings, and his rightly-guided successors always followed the principle of consultation.
Consultation settles many affairs among Muslims. Judges who cannot decide cases employ consultation to reach a verdict, based on the Qur’ān and the Sunnah, thus making it similar to ijtihād (deducing new laws through reasoning based on the Qur’ān and Sunnah) and qiyās (analogy). Furthermore, any punishment of a secondary nature that is not explicitly mentioned in the Qur’ān and the Sunnah can be pronounced after consulting authoritative Muslim jurists.