The Prophet ﷺ said that Allah said, "I have prepared for My righteous servants what no eye has seen, no ear has heard, and what has never crossed the heart of any human being. This is treasured up for them, beyond all that I have shown you."
حدثنا عبد الرحمن بن مهدي قال حدثنا سفيان عن الأعمش عن أبي صالح
أن النبي ﷺ قال قال الله عز وجل أعددت لعبادي الصالحين ما لا عين رأت ولا أذن سمعت ولا خطر على قلب بشر ذخرا بله ما أطلعكم عليه
Its isnad is sahih, it occurred previously at 9614. His saying "tillah, had he not informed you of it" means, except that he did not inform you of this blessing, but rather kept it as a reserve. Many said tillah means "leave," but I did not find that acceptable.