Article 43: The conditions for the assistant are the same as the conditions for the Khalifah; in other words, to be male, free, Muslim, adult, sane, just; and he is from the people of the capability in whatever actions were delegated to him.
The evidence here is the evidence for the Khalifah, so it is obligatory for him to be a male due to words of the Prophet
«لَنْ يُفْلِحَ قَوْمٌ وَلَّوْا أَمْرَهُمُ امْرَأَةً»
“Never will succeed such a nation that makes a woman their ruler.” (reported by Al-Bukhari from Abu Bakrah).
He must be a Muslim due to His words
((وَلَنْ يَجْعَلَ اللَّهُ لِلْكَافِرِينَ عَلَى الْمُؤْمِنِينَ سَبِيلًا (141)))
“And never will Allah give the disbelievers over the believers a way [to overcome them].” (TMQ 4:141); therefore, it is forbidden for a non-Muslim to be a ruler over the Muslims, since ruling is the greatest way over the Muslims.
He is to be free since the slave does not have control over his own issues and so he cannot undertake the control of other peoples’ affairs.
He should be an adult, due to the words of the Messenger
«أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ رُفِعَ الْقَلَمُ عَنْ ثَلَاثَةٍ عَنْ النَّائِمِ حَتَّى يَسْتَيْقِظَ وَعَنْ الصَّغِيرِ حَتَّى يَكْبَرَ وَعَنْ الْمَجْنُونِ حَتَّى يَعْقِلَ أَوْ يُفِيقَ»
“The Messenger of Allah said, “The Pen has been lifted from three (their actions are not recorded) : from the sleeping person until he awakens, from the minor until he grows up, and from the insane person until he comes to his senses.” and in a narration
«وَعَنْ الْمُبْتَلَى حَتَّى يَبْرَأَ»
“and from the afflicted person until he recovers” (reported by Ibn Maja and Al-Hakim from ’Aishah, and the wording is from Ibn Maja). Al-Tirmidhi and Ibn Khuzaima reported the same from Ali.
From the raising of the pen is that his actions in his own affairs are not valid, and so it is not valid for him to act in the affairs of others. In addition, the narration of Abu ’Uqayl Zuhra Bin Ma’bad from his father ’Abd Allah b. Hisham who was at the time of the Prophet when his mother Zaynab Bin Humayd took him to the Messenger of Allah and said: O Messenger of Allah, take Bay’a from him. He replied
«هُوَ صَغِيرٌ، فَمَسَحَ رَأْسَهُ وَدَعَا لَهُ»
“He is a little child, and he passed his hand over his head and invoked Allah for him.” as reported in Al-Bukhari. So as long as the child is not permitted to give the Bay’a, then by greater reasoning, he cannot accept it.
As for being sane, this is due to the narration just mentioned
«رفع القلم عن ثلاثة ...»
“The pen is lifted from three (their actions are not recorded)” until it was mentioned
« وَعَنْ الْمَجْنُونِ حَتَّى يَعْقِلَ أَوْ يُفِيقَ »
“and from the insane person until he comes to his senses” and in a report
«وَعَنْ الْمُبْتَلَى حَتَّى يَبْرَأَ»
“and from the afflicted person till he recovers”. From the raising of the pen is that his actions in his own affairs are not valid and so it is not valid for him to act in the affairs of others.
He should be just, since Allah (swt) made it a condition for the witnessing, saying
((وَأَشْهِدُوا ذَوَيْ عَدْلٍ مِنْكُمْ))
“And take for witness two persons from among you.” (TMQ 65:2), and so it is a condition for the assistant by greater reasoning.
It is a condition for the assistant to be from the people of sufficiency in the actions of ruling since that is necessitated from undertaking ruling, since the one who was not capable would not be able to carry it out. And also due to the evidence mentioned, including: Muslim reported through Abu Dharr:
«قُلْتُ: يَا رَسُولَ اللَّهِ، أَلاَ تَسْـتَـعْمِلُنِي؟ قَالَ: فَضَرَبَ بِيَدِهِ عَلَى مَنْكِبِي ثُمَّ قَالَ: يَا أَبَا ذَرٍّ، إِنَّكَ ضَعِيفٌ، وَإِنَّهَا أَمَانَةُ، وَإِنَّهَا يَوْمَ الْقِيَامَةِ خِزْيٌ وَنَدَامَةٌ، إِلاَّ مَنْ أَخَذَهَا بِحَقِّهَا وَأَدَّى الَّذِي عَلَيْهِ فِيهَا»
“I said: O Messenger of Allah, will you not use me? He placed his hand upon my shoulder and then said O Abu Dharr, you are weak, and it is an Amanah (trust), and on the Day of Judgement, it will be a disgrace and a regret except (for those) who take it by its right and perform its duties correctly”.
The Messenger of Allah considered taking it without its right, in other words, if the person was not suitable for it, would be a disgrace and regret, which is an indication upon the decisiveness of the order.