Souls are definitely created things, although I do not know the mystery of how Allahu ta alaa made them nor what he created them from. I only know that ALL THINGS, except Allahu ta alaa Himself, are created things. That necessarily includes the souls.
But I can substantiate my claims directly from the Qur‘an....
“When your Lord drew forth from the children of Adam - from their loins - their descendants, and made them testify concerning themselves, (He said), ‘Am I not your Lord?‘, they said, ‘Yes! We do testify!‘ Lest you should claim on the Day of Resurrection, ‘Truly, we were heedless of this.‘ Or lest you should claim, ‘Our fathers before us may have taken false gods, but we are their descendants after them. Will You destroy us because of what false and worthless men did?‘ Thus do We explain the signs in detail, that perchance they may return.” Surat-ul-Araaf (7), ayat 172-174.
Now, if you read the ibn Kathir tafseer on the above ayah, you will find a reference to a hadith wherein the Prophet (alaihi salaam) explained that Allahu ta alaa extracted all the souls of Father Adam‘s offspring from Adam‘s spine and presented Himself to them. Then He asked them “Am I not your Lord?” And they were obliged to give the First Shahada, “Yes! We do testify!”
So, we know that Allah created Adam from dirt and water, and then breathed His Rooh (Spirit) into him to give him life, (15:29). After that, Allah was able to extract all of the souls from Adam‘s spine. Clearly, those souls existed within Adam and were residing within him. Logic tells us, then, that the souls came into being when Allah gave life to Adam.
We also know from the Qur‘an that there is nothing in existence that is similar to Allah (6:103; 16;74; 112:4). Allah is Eternal (As‘Samad, 112) from past to future - nothing other than Allah is Eternal. That alone tells us that the souls must be created things, because EVERYTHING other than Allah is created.
I hope ths answer satisfies you.