Has Allah protected the Hadith from corruption and changes? If not, how can we be sure that they are sayings of Prophet $Muhammad$$ (Sallallahu Alaihi wa Sallam), or of someone else?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Allah informs us in the Qur'an that He will perfect His Light. He Says (interpretation of meaning):{…but Allâh will not allow except that His Light should be perfected even though the Kâfirûn (disbelievers) hate (it). }[9:32]. The Light of Allah is His religion, which He has chosen for His servants, which He obliged them to follow and in which He put their welfare. The only true religion is the one that Allah revealed to His Messenger, Muhammad (Sallallahu Alaihi wa Sallam) and its basic sources are the Qur'an and the Sunnah. Allah Says (interpretation of meaning) addressing His Prophet (Sallallahu Alaihi wa Sallam):{…Allâh has sent down to you the Book (The Qur'ân), and AlHikmah (Islâmic laws, knowledge of legal and illegal things i.e. the Prophet's Sunnah - legal ways),… }[4:113]. The Book is the Qur'an and the wisdom is the Sunnah. Both are the sources of this religion, which Allah promised to perfect and protect. Allah Says (interpretation of meaning):{…This day, I have perfected your religion for you, completed My Favour upon you, and have chosen for you Islâm as your religion….}[5:3]. As for the Saying of Allah,{Verily We: It is We Who have sent down the Dhikr (i.e. the Qur'ân) and surely, We will guard it (from corruption). } [15:9]. This verse does not imply the protection of the Qur'an alone, it also implies the protection of the Sunnah as well, because the word 'Reminder' means the Qur'an and the Sunnah. Ibn Hazm said in his book "al-Ihkaam": Adh-Dhikr (Reminder) is a name that comprises all that Allah revealed to His Prophet (Sallallahu Alaihi wa Sallam) be it the Qur'an or the Sunnah. The Sunnah is also a revelation that explains the Qur'an . To indicate that the Sunnah explicates the Qur'an, Allah Says (interpretation of meaning):{…And We have also sent down unto you (O Muhammad SAW) the reminder and the advice (the Qur'ân), that you may explain clearly to men what is sent down to them, and that they may give thought. }[16:44]. Therefore, if anyone claims that the Sunnah's explication of the Qur'an is not protected or that its safety from corruption is not guaranteed, he has rendered the Qur'anic texts as useless and by extension, most obligatory acts of worship like prayer, Zakah, Hajj and fasting. This, however, is impossible. Allah's protection of the Qur'an necessitates His protection of the Sunnah, for the Sunnah is its protective fortress, its strong shield and its trustworthy guard. It is the Sunnah that casts light on the equivocal verses of the Qur'an, limits the injunctions of the unlimited verses and explains in detail what its abstracted verses. All the above does not in any way mean that the Sunnah has not been subjected to vicious attacks by forgers and liars with an intention to cause corruption in the religion or to achieve monetary benefits or to curry the favour of rulers or to support a Madh'hab to which the forger belongs. But Allah appointed some of His servants who refuted their forgeries, exposed their tricks and sorted out their fabrications and rendered them useless. Then, nothing remained but that which benefit people of authentic Sunnah. Among those whom Allah appointed to purify the Sunnah and distinguish the authentic Ahadith from the forgeries are: - Imam Al-Bukhari who was a rock in terms of his exceptional memory. He was also the world leader in the science of Hadith. He is followed by Imam Muslim . There are no weak Hadith in their collections by the grace of Allah. Thus the scholars examined every narration that reached them until the Sunnah of the Prophet (Sallallahu Alaihi wa Sallam) became clear to all. You can avoid weak and spurious Ahadith by reading only the collections of Al-Bukhari and Muslim . You can also read the books of erudite and sagacious past and contemporary scholars, such as Riyaadus-Saaliheen, by An-Nawawi and the translated books of Sheikh Al-Albaani . Allah knows best.