A leader in Islam is called the 'Wali-e-Amr', one who holds the authority. He leads the society and the political porcess. He is the guardian of all legislation. We will discuss the role of consultation with respect to the leader. To understand this, we should look at the two kinds of laws in Islam.
1) Those that have come in Shari'at and that are forever, like the wujub of Hajj and Salat, are called Ahkaam -e-Kulli'. For this first type of Islamic laws, consultation is not an option. For example, the Prophet does not consult the people regarding laws of hajj and salat.
2)Those laws legislated by the Islamic leader regarding a particular time and situation. These are called 'Ahkam-e-juzia'. Examples are whether or not to engage in a defensive war, relations with another state, etc. For the second kind of Islamic laws, Islam has laid down a process for decision-making. Wali-e-Amr sometimes consults experts in the ahkam-e-juzia.
For these laws to have shar'i and legal status, they should be in conformity with the 'maslehat' of people, and determination of this conformity in every legislation requires deep and broad understanding. Such a knowledge is unattainable for any single individual. Wali Amr or ruler or leader of a community is one human being and cannot be an expert in more than one or two sciences unless he is a Ma'sum.
Since he does not have expertise in all sciences he has to consult with experts, specialists in the respective fields. He only consults with those experts who are pious; not fasiq or fajir.
Islamic society would therefore have many shuras which are consulted with respect to their respective areas. Haakim will consult with the body of experts to determine the best course of action to achieve desired results.
Once consultation is done, the Haakim:
1) either attains 'yaqeen' about the best option; in this case he will put the law into implementation and action whether the majority supports it or not,
2) or Haakim does not attain yaqeen; in this case he will accept the opinion which has more solid arguments or evidence,
3) or the two options or more have equally strong arguments or weight; in this situation he will accept the majority's decision if he deems appropriate since he is the most 'alam'(most knowledgeable) and 'atqa'(most Godwary) which means his endorsement is ncessary.
References:
In Surah Naml, verses 29-32:
قَالَتْ يَا أَيُّهَا المَلَأُ إِنِّي أُلْقِيَ إِلَيَّ كِتَابٌ كَرِيمٌ {29}
She said: O chief! surely an honorable letter has been delivered to me
إِنَّهُ مِن سُلَيْمَانَ وَإِنَّهُ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ {30}
Surely it is from Sulaiman, and surely it is in the name of Allah, the Beneficent, the Merciful;
أَلَّا تَعْلُوا عَلَيَّ وَأْتُونِي مُسْلِمِينَ {31}
Saying: exalt not yourselves against me and come to me in submission.
قَالَتْ يَا أَيُّهَا المَلَأُ أَفْتُونِي فِي أَمْرِي مَا كُنتُ قَاطِعَةً أَمْرًا حَتَّى تَشْهَدُونِ {32}
She said: O chiefs! give me advice respecting my affair: I never decide an affair until you are in my presence.
In Surah Baqarah, verse 233:
وَالْوَالِدَاتُ يُرْضِعْنَ .............
2:233 And the mothers should suckle their children for two whole years for him who desires to make complete the time of suckling; and their maintenance and their clothing must be-- borne by the father according to usage; no soul shall have imposed upon it a duty but to the extent of its capacity; neither shall a mother be made to suffer harm on account of her child, nor a father on account of his child, and a similar duty (devolves) on the (father's) heir, but if both desire weaning by mutual consent and counsel, there is no blame on them, and if you wish to engage a wet-nurse for your children, there is no blame on you so long as you pay what you promised for according to usage; and be careful of (your duty to) Allah and know that Allah sees what you do.
In Surah Talaq, verse 6:
أَسْكِنُوهُنَّ مِنْ حَيْثُ سَكَنتُم مِّن وُجْدِكُمْ وَلَا تُضَارُّوهُنَّ لِتُضَيِّقُوا عَلَيْهِنَّ وَإِن كُنَّ أُولَاتِ حَمْلٍ فَأَنفِقُوا عَلَيْهِنَّ حَتَّى يَضَعْنَ حَمْلَهُنَّ فَإِنْ أَرْضَعْنَ لَكُمْ فَآتُوهُنَّ أُجُورَهُنَّ وَأْتَمِرُوا بَيْنَكُم بِمَعْرُوفٍ وَإِن تَعَاسَرْتُمْ فَسَتُرْضِعُ لَهُ أُخْرَى {6}
Lodge them where you lodge according to your means, and do not injure them in order that you may straiten them; and if they are pregnant, spend on them until they lay down their burden; then if they suckle for you, give them their recompense and enjoin one another among you to do good; and if you disagree, another (woman) shall suckle for him.
In Surah Aale Imran, verse 159:
فَبِمَا رَحْمَةٍ مِّنَ اللّهِ لِنتَ لَهُمْ وَلَوْ كُنتَ فَظًّا غَلِيظَ الْقَلْبِ لاَنفَضُّواْ مِنْ حَوْلِكَ فَاعْفُ عَنْهُمْ وَاسْتَغْفِرْ لَهُمْ وَشَاوِرْهُمْ فِي الأَمْرِ فَإِذَا عَزَمْتَ فَتَوَكَّلْ عَلَى اللّهِ إِنَّ اللّهَ يُحِبُّ الْمُتَوَكِّلِينَ {159}
Thus it is due to mercy from Allah that you deal with them gently, and had you been rough, hard hearted, they would certainly have dispersed from around you; pardon them therefore and ask pardon for them, and take counsel with them in the affair; so when you have decided, then place your trust in Allah; surely Allah loves those who trust.
The above mentioned ayah was discussed in detail in the previous sermon of 'Gentleness of the Prophet'.
In Surah Shura, verses 36-49:
فَمَا أُوتِيتُم مِّن شَيْءٍ فَمَتَاعُ الْحَيَاةِ الدُّنْيَا وَمَا عِندَ اللَّهِ خَيْرٌ وَأَبْقَى لِلَّذِينَ آمَنُوا وَعَلَى رَبِّهِمْ يَتَوَكَّلُونَ {36}
So whatever thing you are given, that is only a provision of this world's life, and what is with Allah is better and more lasting for those who believe and rely on their Lord.
وَالَّذِينَ يَجْتَنِبُونَ كَبَائِرَ الْإِثْمِ وَالْفَوَاحِشَ وَإِذَا مَا غَضِبُوا هُمْ يَغْفِرُونَ {37}
And those who shun the great sins and indecencies, and whenever they are angry they forgive.
وَالَّذِينَ اسْتَجَابُوا لِرَبِّهِمْ وَأَقَامُوا الصَّلَاةَ وَأَمْرُهُمْ شُورَى بَيْنَهُمْ وَمِمَّا رَزَقْنَاهُمْ يُنفِقُونَ {38}
And those who respond to their Lord and keep up prayer, and their rule is to take counsel among themselves, and who spend out of what We have given them.
وَالَّذِينَ إِذَا أَصَابَهُمُ الْبَغْيُ هُمْ يَنتَصِرُونَ {39}
And those who, when great wrong afflicts them, defend themselves.