Assalaamu alaykum wa rahmatullaahi wa barakaatuh. Can I follow someone to see where he lives so that I can intentionally take position on his route and talk to him (asking how he is, etc.)? Then I can become his friend and give this Muslim religious advice because he is indecent.
All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
The objective you are seeking to accomplish is noble and valid; offering sincere advice to fellow Muslims is one of the noblest duties and the best righteous deeds that draw the person closer to Allah. Tameem Ad-Daari narrated that the Prophet, sallallaahu ʻalayhi wa sallam, said, “The religion is (founded on the exchange of sincere) advice.” They said, “For whom?” He, sallallaahu ʻalayhi wa sallam, replied, “For Allah, His Book, His Messenger, and for the leaders of the Muslims and their masses.” [Muslim]
Accomplishing this does not require all that you mentioned in the question of following him, finding out where he lives, and standing on his route etc. It is sufficient that when you meet him anywhere, you greet him with the Salaam and kindly and gently advise him.
However, if you need to do what you mentioned in order to get closer to him and win his trust so that he would accept your advice, then there is no harm in that, Allah Willing. Nevertheless, you should beware of violating the privacy of his household, which is forbidden in Islam.
Allah knows best.
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