How did the righteous predecessors infer that God's intrinsic attributes are eternal and everlasting?

God's intrinsic attributes are eternal and everlasting; He is characterized by every perfection and free from every deficiency. It is impossible for His attributes to have originated for Him after they were nonexistent, or for a time to come when He is not characterized by them, for that would entail a deficiency unfitting for Him. Al-Tahawi said: "He has ever been, with His attributes, eternal before His creation. He did not gain anything through their existence that was not already among His attributes before them. Just as He has ever been, with His attributes, eternal, so too will He remain upon them eternally." Ibn Abi al-Izz clarified that God has always been characterized by the attributes of perfection, and it is impermissible to believe that He acquired an attribute after not possessing it, because the absence of these attributes is a deficiency unfitting for Him.