And how did the Prophet s.a.w react in regards to Musaylimah the false prophet
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I'm pretty sure if the Prophet s.a.w was among us today he would say the same about Ghulam Ahmed Mirza
You just contradicted yourself
Abu Said al-Khudri reported: 'Ali b. Abu Talib sent to the Messenger of Allah (may peace be upon him) from Yemen some gold alloyed with clay in a leather bag dyed in the leaves of Mimosa flava. He distributed it among four men. 'Uyaina b. Hisna, Aqra' b. Habis and Zaid al-Khail, and the fourth one was either Alqama b. 'Ulatha or 'Amir b. Tufail. A person from among his (Prophet's) Companions said: We had a better claim to this (wealth) than these (persons). This (remark) reached the Apostle of Allah (may peace be upon him) upon which he said: Will you not trust me, whereas I am a trustee of Him Who is in the heaven? The news come to me from the heaven morning and evening. Then there stood up a person with deep snnken eyes, prominent cheek bones, and elevated forehead, thick beard, shaven head, tucked up loin cloth, and he said: messenger of allah, fear allah. He (the Holy Prophet) said: Woe to thee. do I not deserve most to fear Allah amongst the people of the earth? That man then returned. Khalid b. Walid then said: Messenger of Allah, should I not strike his neck? Upon this he (the Holy Prophet) said: Perhaps he may be observing the prayer. Khalid said: How many observers of prayer are there who profess with their tongue what is not in their heart?
Upon this the Messenger of Allah (may peace be upon him) said: I have not been commanded to pierce through the hearts of people, nor to split their bellies (insides). He again looked at him and he was going back. Upon this he (the Holy Prophet) said: There would arise a people from the progeny of this (man) who would recite the Qur'an glibly, but it would not go beyond their throats; they would (hurriedly) pass through (the teachings of their) religion just as the arrow passes through the prey. I conceive that he (the Holy Prophet) also said this: If I find them I would certainly kill them as were killed the (people of) Thamud.
(Book #005, Hadith #2319)
This man was Dhul Khuwaisirah Al Tamimie, The Prophet (saw) knows that he is khawaarij, and that from his children will be khawaarij, and that he conceals kufr, but he judged his imaan on his sayings and his actions, not from what was in his heart. Imam Ali killed thousands from the khawaarij, but only after they made takfeer upon and killed one sahabi - Abdullah ibn Khabbab. He did not judge their hearts, rather he judged them when they committed actions and made takfeer on them when they did, despite that they do believe and testify that "laa ilaaha illallah".
Khalid bin Waleed learnt from this that he should not judge someone by intention, but rather by his actions. This helped him in the time of Musailamah Kazab, who used to claim to be the brother of Muhammad and another messenger. Musailamah even used to try to make ayat, similar to the Qur'an. However even his own followers told him that it is better to repeat the ayat of Muhammad, and that they will accept it from him, because his own verses were so obviously defective.
Muja'a was a man who spent some time accompanying the Prophet (saw), and he was from the same town as Musailamah. Khalid bin Waleed was the one who was sent to fight against Musailamah, he conquered, and he captured from them 20 apostates. Muja'a said to him: "
Assalamu 'Alaikum Wa Rahmatullah." Khalid looked to him and said: "Now you give me salaam?" Muja'a said: "O kahlid you know me, I was among them who gave baya'ah to Muhammad (saw) and I still believe in what I believed in the past …"Khalid said: "you do not believe in what you believed in the past, and your acceptance to live under this False Prophet (Musailamah kazab) and your silence is your consent. You are the most noble man in Yamamah, you knew that I was coming, yet you stayed with him and you did not come out with me, I cannot find any excuse for you at all, you heard what they said and you did not say a word, and there were among you people less than you, and they spoke against Musailamah, and they have been tortured and had been killed." Muja'a said: "I was fearing from my people," Khalid said: "Why did you not come to me or send me a letter, I am going to stop killing you, but I am not going to let you free, between releasing you from my sword and releasing you completely is a middle solution, I am going to imprison you until Allah finds us a way."
He (Khalid bin Waleed) consulted with other sahabah and he killed Muja'a, because he judged his kufr actions NOT his intention.
Imam Shaafi' said about this: "Khalid bin Waleed considered Muja'a kafir because he was silent and he left what he believed in the past."