What is the ruling on obeying one who abandons prayer, and how should one deal with them, and what is the ruling on greeting them with peace, and is it permissible to address them with titles such as "Amir" or "Sayyid"?

In summary, regarding one who abandons prayer, if they abandon it out of denial, they are considered an apostate. However, if they abandon it out of laziness, there is a difference of opinion: some jurists consider them an apostate, while others do not. There is also an opinion that differentiates between one who completely abandons prayer and one who prays sometimes and abandons it sometimes.

As for dealing with one who abandons prayer, if their repentance is hoped for through advice, they should be advised and reminded of Allah. If their repentance is hoped for through boycotting, they should be shunned, not spoken to, and not greeted with salam.

Regarding marrying one who abandons prayer, it is not permissible to marry them to a Muslim woman until they repent and pray, especially if they abandon it completely, because they are not pleasing in their religion.

Furthermore, one who abandons prayer should not be addressed with any terms of glorification because they are a fasiq (transgressor). Al-Nawawi mentioned in Riyad al-Salihin a chapter on the prohibition of addressing a fasiq, an innovator, and the like with "master" or similar terms, and he cited the hadith: "Do not say to a hypocrite, 'Master,' for if he were a master, you would have angered your Lord, the Exalted."