Sunan Ibn Majah #3117 · Chapters on Hajj Rituals

“Whoever is in Makkah when the month of Ramadan comes, and he fasts it and prays at night as much as he can, Allah will record for him (reward equivalent to that for) one hundred thousand months of Ramadan observed elsewhere. For each day Allah will record for him (reward equivalent to that for) freeing a slave, and for each day (reward equivalent to that for) providing a horse in the cause of Allah, and for every day merits and for every night merits.”