As-Salaam alaikum,
Indeed, that Hadith Qudsi quoted on/about fasting being Allah's is right on target... whereby Allahu, Subhanahu Wa Ta'ala, says:--
"Fasting is Mine, and I have the best right to give recompense for it.."(al-saum li wa-ana ajza bihi). And this is because the religious practice of fasting is a mystery unconnected with any external thing, a mystery in which none other than Allah participates: hence the recompense is infinite.
ALLAHU AKBAR! ALLAHU AKBAR!! WA-LILLAHIL HAMD...