In the Name of Allah, the Extremely Merciful, the Bestower of Mercy
Imaam as-Sa`dee (d. 1376 AH), may Allah have mercy upon him, said:1
5. To bear witness that Muhammad is the Messenger of Allah entails that the servant believes that Allah sent Muhammad ﷺ to all of ath-thaqalayn (jinn and man) as a bearer of glad tidings and a warner, calling to the oneness of Allah and His obedience.
He must believe in all what he [ﷺ] has informed of; obey his commandments and keep from his prohibitions. [He must believe] that there is no felicity or
good in this world or in the Hereafter except by having faith in and obeying him. It is obligatory that the [servant's] love for him takes precedence over love for himself, his children, and all of mankind.
He must believe that Allah has aided him with miracles that are indicative of his Messenger-ship. He must believe that Allah has fashioned him with complete knowledge and an exalted standard of character; and he must believe in what his religion is comprised of from guidance, mercy, truth, religious and worldly good.
He must believe in his main sign, the Great Qur.aan, and in what it contains of truth, commandments, and prohibitions. And Allah knows best.
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Translated by Umm Sufyaan Faatimah
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[1] Imaam `Abdur-Rahmaan as-Sa`dee, Manhaj as-Saalikeen wa Tawdeeh al-Fiqh fīd-Deen, p11-12.