Allah says: “Lest a person should say: "Alas, My grief that I was undutiful to Allah (i.e. I have not done what Allah has ordered me to do), and I was indeed among those who mocked [at the truth! i.e. Lâ ilâha ill-Allah (none has the Right to be worshipped but Allâh), the Qur’an, and Muhammad Sal-Allaahu 'alayhe Wa Sallam and at the faithful believers, etc.]” [al-Zumar 39:56] What is meant by Janbi-llah and is it a quality from the qualities of Allah and how do we affirm it? المقصود بقوله تعالى جنب الله

Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.

As to what follows:

With regards to answering your question we say, success is by Allah Almighty.

Scholars have several opinions regarding the meaning of Janbi-llah.

Some say it means the right of Allah, others say it means the matter of Allah, others say it means the side of Allah, it is also said that adding the side to Allah does not necessitate it being a quality of Allah.

Ibn Taymiyah said in Al-Jawab al-sahih liman badala deen al-maseeh (4/416): “created things and their qualities may be added to Allah but they won’t be part of Allah’s qualities, like house of Allah, she-camel of Allah or servants of Allah …” then he said:

It is clarified in the Quran that what is meant by Janbi-llah is not similar to the side of a human being, for the Quran says:

“Lest a person should say: "Alas, My grief that I was undutiful to Allah (i.e. I have not done what Allah has ordered me to do)”[al-Zumar 39:56]

Being undutiful does not have anything to do with Allah’s qualities. What is clear from the words of Ibn Taymiya is that Janbi-llah is not a quality of Allah, not only that but he mentioned in Fatawa (6/14) that the verse does not imply Allah’s quality:

Some of the people who affirm Allah’s qualities say that here the verse implies Allah’s quality, since they see other texts implying qualities. They take every verse which purports an addition to Allah’s name as an addition of Allah’s quality, like the verse(Janbi-llah [undutiful to Allah]), but this verse is not from the verses which imply Allah’s qualities.
And Allah knows best.