How sound is the popular saying: "A morsel in the mouth of a hungry person is better than building a thousand mosques"?

The saying "A morsel in the belly of a hungry person is better than building a thousand mosques" is not a prophetic hadith, and its meaning is invalid. Building a single mosque is fundamentally better than feeding the hungry, because a mosque achieves general and far-reaching religious benefits and is an ongoing charity (sadaqa jariya), whereas feeding the hungry achieves a worldly benefit for a limited group and is usually not ongoing.

However, if the two matters conflict and cannot be combined, then the one that is more beneficial is prioritized. Feeding the hungry may be accompanied by circumstances that make it better, such as when people are in a severe famine or war, in which case feeding them would be more deserving than building a mosque.