It is a contractual condition for the Caliph to be upright/just/trustworthy (‘Adl) and it is not allowed for him to be a transgressor (fasiq). The evidence for this contractual condition is from the Qu’ran where Allah سبحانه وتعالى stipulates that a witness must be upright.

 وَأَشْهِدُوا ذَوَيْ عَدْلٍ مِنْكُمْ 

“Call two upright (‘Adl) men from among yourselves as witnesses” 

 (At-Talaq, 65:2)

So if the witness must be upright, then the Caliph who holds a higher post and governs over the witness should, by greater reason (Bab Awla), be upright.

What does the word ‘Adl mean? 

Ahmad ad-Da’our answers the question in his book, Ahkaam al-bayyinaat (The Rules of Testimonial Evidences) an extract of which follows.

Trustworthiness (‘Adl) means that transgression (fisq) does not appear from him. The one who is faasiq that shows his transgression (fisq); his testimony is not accepted. But the one whose fisq was not apparent, his testimony would be accepted. There is a disagreement regarding the definition of ‘adl. It is said that ‘adl refers to a person who is no known t have committed any kabeerah (grave) sin or openly committed a (minor) sagheerah sin. This definition is ambiguous because the definition of kabeerah sin is not agreed upon. It is not even agreed that there is something called kabeerah and sagheerah sin because no sin is small. The violation of Allah’s command is big whether it is lying or giving false testimony. As for what was mentioned in the text that there are kabeerah sins, what’s meant is to stress the prohibition. Otherwise we find there are sins which are bigger but we do not find them being described as kabeerah. It has been stated in the text that false testimony is kabeerah, but it has not been stated that highway robbery is kabeerah. False testimony is one type of a lie, but to give a lie to the Messenger of Allah ﷺ was not mentioned within the kabeerah sins. So, there is no defining limit to the kabeerah or the sagheera sin such that one can say someone is known to have committed a kabeerah sin or displayed a sagheerah sin. Thus, the definition is not clear. What is better is that we should say ‘adl is the person who restrains himself from that which the people would consider in breach of upright behavior. This is because the word ‘adl in respect to witnesses has been mentioned in two verses of the Qur’an:

 يَا أَيُّهَا الَّذِينَ آمَنُوا شَهَادَةُ بَيْنِكُمْ إِذَا حَضَرَ أَحَدَكُمُ الْمَوْتُ حِينَ الْوَصِيَّةِ اثْنَانِ ذَوَا عَدْلٍ مِنْكُمْ 

“O you who believe! When one of you is near to death and makes a will, two just men from among you should act as witnesses” 

 (Al-Maaida, 5:106)

 وَأَشْهِدُوا ذَوَيْ عَدْلٍ مِنْكُمْ 

“Call two upright men from among yourselves as witnesses” 

 (At-Talaq, 65:2)

 It is one of the expressions used by the Qur’an and therefore, so it is not given a technical or an arbitrary explanation, rather it should be interpreted the way other words and sentences of the Qur’an are interpreted. Thus, it is explained by its linguistic meaning if it does not have another shar’i meaning mentioned in the Kitaab and Sunnah. If it has ashar’i meaning then it is interpreted according to the shar’i meaning. Upon scrutiny we do not find a special meaning mentioned by the Legislator for the word ‘adl in respect to witnesses other than its linguistic meaning, and hence it needs to be explained according to its linguistic meaning. The word ‘adl in respect to witnesses means in the Arabic language someone who is known by the people to be of upright character. It says in al-Qamoos al-Muheet: ‘al-‘adl is the opposite of jawr (injustice), and it is that which is established in the souls of people as being upright (mustaqeem), such as reliability (‘adala), and relaiable (‘adool). It comes from ‘adala, ya’dilu, so he is ‘aadil (he was just, so he is just). ‘Adala al-hukm (he established the judgenment). ‘Adal a person (he commended him). ‘Adala the balance (he levelled it)’. This text which gives the meaning of ‘adl in respect to witnesses indicates that the ‘adaalah is istiqaamah (to be of upright character). Defining ‘adl as that which is established in the souls of people as being upright (mustaqeem) is an ambiguous speech. This is because there is no limit by which uprightness is known, for the situations of the people differ, and the people’s habitats also differ in their view to uprightness. Though uprightness means proceeding on the straight path, but this straight path is technical and neither is it linguistic or shar’i. Therefore, it is necessary to refer the explanation of the meaning of the word of uprightness (istiqaama) to the view of the people in accordance with their habitats and societies. This is the approach followed by the linguistic dictionaries specialized in the explanation of the linguistic words that were mentioned regarding the ahkam shar’iyyah. Al-Misbah al-Munir mentioned:

(‘Addaltu ash-shahid ‘I commended the witness’ means ‘I ascribed him to ‘adaala (trustworthiness) and portrayed him with it). The term of ‘adl applies to one or more, and its plural as ‘udool, as it came in poem of Abul Abbas as mentioned by Ibn al-Anbari:

Ta’aaqada al-‘aqda al-watheeqa wa-ashhada 

Min kulli Qawmin Muslimeena ‘udoola 

They convened the strong covenant and sought witness

From every folk, Muslims and trustworthy

In the feminine, it might be said imra’ah ‘adlah (a trustworthy woman). Some scholars said that ‘adaala is an attribute which requires abstaining from anything that usually violates the sense of honour (muroo’a) openly. However, one small mistake and twisting the words once does not violate the sense of honour openly, for it is possible that was because of forgetfulness or interpretation. This is different to the case when this became widely known and repeated, then violation becomes open. The norm ‘’urf’ of every person is that which he is used to in terms of dress, dealings in trading and carrying his luggage and the like; so if he did that which is impropriate to him, unnecessarily, then he violated his muroo’a, otherwise not). This text from this dictionary differs according to the people habitats. This is because the word of uprightness is ambiguous, thus leading to this difference. However, it might be referred to the linguistic explanation of the word of (‘adl) and thus adopt the meaning of the explanation. So, their saying: (That which is established in the souls as being upright) would mean the one that is not known about him of openly violating that which the people consider impropriate. Therefore, it is better to say ‘adl is the one that abstains from that which the people considers violation of uprightness, whether he was a Muslim or non-Muslim. This is because ‘adaala was stipulated in the testimony of the Muslim as well as in the testimony of the non-Muslim, by using the same word without distinguishing one from the other. Allah سبحانه وتعالى said:

يا أَيُّهَا الَّذينَ آمَنوا شَهادَةُ بَينِكُم إِذا حَضَرَ أَحَدَكُمُ المَوتُ حينَ الوَصِيَّةِ اثنانِ ذَوا عَدلٍ مِنكُم أَو آخَرانِ مِن غَيرِكُم

“O you who believe! When one of you is near to death and makes a will, two just men from among you should act as witnesses, or two others from other than you”

 (Al-Maaida, 5:106)

He سبحانه وتعالى meant non-Muslims by saying “other than you”. He said ‘two ‘adl witnesses from Muslims or two ‘adl from other than Muslims. So, how can the ‘adaala be defined to be not committing a kabeera (major) sin and insistence on committing a sagheera (small) sin regarding a non-Muslim? How we can also reject as witness the one who disobeyed his parents once, but accept as witness the spy, just because spying is not from kabeera sins? Therefore, the valid meaning of ‘adl is the one that abstained from that which the people consider violation to the uprightness. Whoever was characterised with that he is ‘adl, because he is one of those that was established in the souls that he is upright. The one that is known (amongst the people) to be insolent in doing haram or committing sin openly, or reckless about committing it, or known of being not upright, he would be fasiq. Thus ‘adl is opposite to fasiq, and ‘adaala is opposite to fisq. Thus, the fasiq is the one that does not abstain from haram, or known to be not upright. ‘Adl is the one that abstains from haram, or not known to be lacking uprightness.