The Prophet ﷺ used to say that, but he did not say it during the prayer.
حدثنا وكيع حدثنا مسعر حدثنا عبيد بن حسن
أن النبي ﷺ كان يقول ذلك ولم يقل في الصلاة
No references are available.
Its chain is sahih, like the one before it.