This prayer comes at the end of Augustine’s famous de Trinitate (XV.51). As someone whose thoughts don’t ever seem to quit, I hope this encourages you as it did me:
“Deliver me, my God, from much speaking which I suffer inwardly in my soul, which is so wretched in your sight and flies to your mercy for refuge. My thoughts are not silent even when my voice is. And of course, if I thought nothing but what is pleasing to you, I would not ask you to deliver me from this much speaking. But many of my thoughts are of the kind of which you know the thoughts of men that they are vain (Ps 94:11). Grant me not to consent to them, and if ever they delight me grant that I may reject them and not linger over them in a kind of doze. Let them not so prevail over me that any action of mine proceeds from them, but let my judgement at least be preserved from them, and my conscience, with you to preserve me. A wise man was speaking of you in his book which is now called Sirach as its proper name, and he said, We say many things and do not attain, and the sum of our words is, he is all things (Sir 43:27). So when we do attain to you, there will be an end to these many things which we say and do not attain, and you will remain one, yet all in all, and we shall say one thing praising you in unison, even ourselves being also made one in you.
Oh Lord the one God, God the Trinity, whatsoever I have said in these books is of you, may those that are yours acknowledge, whatsoever of myself alone, do you and yours forgive.