Narrated ‘Itban bin Malik:
who was one of the companions of Allah’s Apostle and one of the Ansar’s who took part in the battle of Badr: I came to Allah’s Apostle and said, “O Allah’s Apostle I have weak eyesight and I lead my people in prayers. When it rains the water flows in the valley between me and my people so I cannot go to their mosque to lead them in prayer. O Allah’s Apostle! I wish you would come to my house and pray in it so that I could take that place as a Musalla. Allah’s Apostle said. “Allah willing, I will do so.” Next day after the sun rose high, Allah’s Apostle and Abu Bakr came and Allah’s Apostle asked for permission to enter. I gave him permission and he did not sit on entering the house but said to me, “Where do you like me to pray?” I pointed to a place in my house. So Allah’s Apostle stood there and said, ‘Allahu Akbar’, and we all got up and aligned behind him and offered a two-Rak’at prayer and ended it with Taslim. We requested him to stay for a meal called “Khazira” which we had prepared for him. Many members of our family gathered in the house and one of them said, “Where is Malik bin Al-Dukhaishin or Ibn Al-Dukhshun?” One of them replied, “He is a hypocrite and does not love Allah and His Apostle.” Hearing that, Allah’s Apostle said, “Do not say so. Haven’t you seen that he said, ‘None has the right to be worshipped but Allah’ for Allah’s sake only?” He said, “Allah and His Apostle know better. We have seen him helping and advising hypocrites.”
Allah’s Apostle said, “Allah has forbidden the (Hell) fire for those who say, ‘None has the right to be worshipped but Allah’ for Allah’s sake only.”
Whoever declares ‘la ilaha illa Allah‘, is officially a Muslim. He/she will be treated as a Muslim. You have no right to judge them and make assumptions about their belief or disbelief. You can’t say that a certain person will definitely go to Hell. Similarly, saying a certain person will definitely go to Jannah is also not right. Allah is the Judge. Not you.