What is the ruling on a man praying at home and not attending congregational prayers at the mosque, and what is the ruling on eating, drinking, and sitting with someone who commands and forbids him in this regard?

One should not sit with a wine-drinker or eat and drink with him, because Allah Almighty says: "And do not incline toward those who do wrong, lest the Fire touch you." Sitting with him without condemning his action is an approval of it, and whoever approves is like one who commits it. It is permissible to sit with him if the goal is to advise and guide him; in fact, it is religiously required for whoever is capable of that. And if eating and drinking with him is hoped to yield positive results, such as encouraging him towards good, or to pray, or to hear good words, then there is no harm in that, because it falls under the general scope of inviting him to Allah, and the caller to Allah should be someone who wins over people to influence them.