What does it mean to say that affirming a divine attribute dictates negation of its opposite?
Question

When Allah states that He is free of an attribute, such as death for example, in that case we must affirm its opposite, which is eternal life in this instance. But what if He ascribes an attribute to Himself, must we negate its opposite?
Praise be to Allah.Firstly:
When Allah states that He is free of an attribute, that negation implies two things:
i.This attribute is not one of His attributes
ii.Its opposite is to be affirmed in the most perfect manner.
Allah, may He be exalted, says (interpretation of the meaning):
“and your Lord treats no one with injustice”
[al-Kahf 18:49].
In this verse, the attribute of injustice or wrongdoing is negated in the case of Allah; at the same time it is an affirmation of its opposite in the most perfect manner. Thus Allah, may He be glorified, does not do any injustice, because of His perfect justice.
The reason for the affirmation in a perfect manner of the opposite of the negated attribute is that negation of an attribute without affirmation of its opposite is nothing, and does not imply perfection. Allah, may He be exalted, does not ascribe to Himself anything that does not imply perfection.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
It should be understood that negation of an attribute does not imply praise or perfection unless it implies an affirmation (of its opposite). Otherwise, mere negation does not convey any sense of praise or perfection, because negation that does not imply something is just nothing, and if it is nothing, it does not mean anything. So, as the saying goes, it is not anything, let alone being praise or perfection. Because negation is something that may be applied to something that does not exist, that which does not exist cannot be described in any sense of praise or perfection.
Most of the attributes that Allah negates with regard to Himself imply affirmation of a positive attribute, such as when He says (interpretation of the meaning):
“Allah! La ilaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists. Neither slumber, nor sleep overtake Him… His Kursee extends over the heavens and the earth, and He feels no fatigue in guarding and preserving them”
[al-Baqarah 2:255].
Negation of slumber and sleep implies life and sustaining in the most perfect sense. Thus it highlights the perfect attributes of the Ever Living, the One Who sustains and protects all that exists. Similarly, His words ‘and He feels no fatigue in guarding and preserving them” mean that it is not too bothersome or too burdensome for Him, which implies the perfect nature of His power, in contrast to any created being that has power, for that created being will only be able to do something with some difficulty and effort, which is a reflection of the imperfection and shortcomings of his power. Similarly, in the verse (interpretation of the meaning):
“not even the weight of an atom (or a small ant) or less than that or greater, escapes from His Knowledge in the heavens or in the earth”
[Saba’ 34:3],
negation of even an atom’s weight escaping His knowledge implies that He has knowledge of every atom in the heavens and on earth, and so on.
End quote from Majmoo‘ al-Fataawa, 3/35, 36
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
Whenever Allah, may He be exalted, negates something with regard to Himself, what is meant is that He does not have that attribute, but it is affirming the opposite attribute in a perfect sense. Negation in this regard is not a negation with no implication, because negation does not indicate perfection unless it implies some perfect attribute. That is because negation is non-existence, and non-existence is nothing, let alone perfection. Moreover, negation may be because of the lack of connection, so it is not perfection, such as if you say: The wall does not wrong anybody, but it has no ability to do that deed, so in that case, negation implies a shortcoming.
End quote from al-Qawaa‘id al-Muthla fi Sifaat Allaah wa Asmaa’ihi al-Husna (p. 23).
See also: Taqreeb at-Tadmuriyyah by Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) (p. 47-50).
Secondly:
The positive attributes that Allah has affirmed with regard to Himself imply two things: affirmation of the divine attribute and negation of the opposite of that which is affirmed with regard to Him, may He be glorified.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
The Muslim should affirm that which must be confirmed for Allah of attributes of perfection, and he must negate that which must be negated with regard to Him of the opposite of those attributes.
End quote from at-Tadmuriyyah (p. 4).
He also said:… The religious texts affirm those divine names and perfect attributes that have been narrated, and whatever is opposite to that, the religious texts negate it, as they negate the notion that He has any equal or peer. Affirmation of a thing is the negation of its opposite, and whatever may be connected to its opposite.
End quote from Majmoo‘ al-Fataawa (3/84).
Shaykh Yoosuf al-Ghufays (may Allah have mercy on him) said: The basic principle in this regard is that every text that affirms an attribute implies that the attribute is to be affirmed and indicates that Allah is to be declared to be above the opposite. Declaring Allah to be above all shortcomings is of two types:
1. Declaring Him to be above all shortcomings in general terms
2. Declaring Him to be above all shortcomings in specific terms.
With regard to the texts that affirm the divine attributes, they are declaring Him to be above all that is not befitting to Him in general terms.
With regard to declaring Him to be above all shortcomings in specific terms, that is appropriate with reference to a specific attribute. In other words, when Allah says (interpretation of the meaning): “And He is the All-Knower of every thing” [al-Hadeed 57:3], that indicates that He is above being ignorant. The verse implies this specific sense of His being above all shortcomings. Moreover, it includes declaring Him to be above shortcomings in general terms, for the One Who has knowledge of all things must be the First, and He must be the Last, and He must be the Lord, and so on…
Every text that affirms any divine attribute implies negation of any similarity or resemblance (of that divine attribute to the attributes of His creation); it implies that He is above having any shortcomings in a specific sense and that He is above having any shortcomings in general terms.
End quote from Sharh at-Tadmuriyyah.
    And Allah knows best.