Belief in Allah and good deeds are a condition for Allah

Allah the Almighty said: ﴾فَمن يَعْمَلْ مِنَ الصَّلِحَتِ وَهُو مُؤْمِنٌ فَلَا كُفْرَانَ لِسَعْيِهِ، وَإِنَّا لَهُ كَتِبُون ﴿ Al-Anbiya: 94]{So whoever does righteous deeds while he is a believer - no denial will there be for his effort, and indeed, We are its recorders.} [ So He made faith a condition along with righteous deeds so that his effort would be appreciated and he would be rewarded for it in the Hereafter.
He explained that polytheism nullifies all deeds, as Allah the Almighty said: ﴾وَلَقَدْ أُوحِيَ إِلَيْكَ وَإِلَى الَّذِينَ مِن قَبْلِكَ لَبِنْ أَشْرَكْتَ لَيَحْبَطَنَّ عَمَلُكَ وَلَتَكُونَنَّ مِنَ الْخَسِرِينَ بَلِ اللَّهَ فَاعْبُدْ وَكُن مِّنَ الشَّكِرِينَ﴿ [Az-Zumar: 65-66] {And it has already been revealed to you, and to those before you, that if you associate others with Allah, your work will surely become worthless, and you will surely be among the losers. Rather, worship Allah and be among the grateful.} .
And the Allah Almighty said, referring to His prophets and messengers: ﴾وَلَوْ أَشْرَكُوا لَحَبِطَ عَنْهُم مَّا كَانُوا يَعْمَلُونَ﴿ [Al-An`am: 88] {And if they had associated others with Allah, all that they used to do would have been in vain} .
And the Allah Almighty said about the deeds of the disbelievers: ﴾وَقَدِمْنَا إِلَىٰ مَا عَمِلُوا مِنْ عَمَلٍ فَجَعَلْنٰهُ هَبَاءً مَنْثُورًا﴿ [Al-Furqan: 23] {And We will present to them whatever deeds they have done and make them as scattered dust} .
Allah also said about the deeds of the infidels:
﴿وَالَّذِينَ كَفَرُوا أَعْمَلُهُمْ كَسَرَابٍ بِقِيعَةٍ يَحْسَبُهُ الظَّمْنَانُ مَاءً حَتَّى إِذَا جَاءَهُ لَمْ يَجِدْهُ شَيْئًا وَوَجَدَ اللَّهَ عِندَهُ فَوَفَّٰهُ حِسَابَهُ وَاللَّهُ سَرِيعُ الْحِسَابِ أَوْ كَظُلُمَاتِ فِي بَحْرِ لُجِّي يَغْشَهُ مَوْجٌ مِن فَوْقِهِ مَوْجٌ مِن فَوْقِهِ سَحَابٌ ظُلُمَٰتُ بَعْضُهَا فَوْقَ بَعْضٍ إِذَا أَخْرَجَ يَدَهُ لَمْ يَكَدْ يَرَٰهَا وَمَن لَّمْ يَجْعَلِ اللهُ لَهُ نُورًا فَمَا لَهُ مِن نُورٍ﴾ [An-Nur: 40:39]
“And those who disbelieve - their deeds are like a mirage in a lowland which a thirsty one thinks is water until, when he comes to it, he finds it is nothing. But he finds Allah with him, and He will pay him his due. And Allah is swift in account. Or [they are] like darknesses within a deep sea which is covered by waves upon waves upon waves - darknesses, one upon another. When he puts out his hand, he can scarcely see it. And whoever disbelieves, he will be disbelieved.” Allah has not given him light, so there is no light for him. .
He explained that death as apostate nullifies one’s deeds in this world and the Hereafter, and leads to eternal damnation to Hellfire, as Allah the Almighty said: ﴾وَمَن يَرْتَدِدْ مِنكُمْ عَن دِينِهِ، فَيَمُتْ وَهُوَ كَافِرٌ فَأَوْلَئِكَ حَبِطَتْ أَعْمَلُهُمْ فِي الدُّنْيَا وَالآخِرَةِ وَأَوْلَئِكَ أَصْحَبُ النَّارِ هُمْ فِيهَا خَلِدُونَ﴿ [Al-Baqarah: 27] “And whoever among you reverts from his religion and dies while he is a disbeliever for those, their deeds have become worthless this world and the Hereafter, and those are the companions of the Fire; they will abide therein eternally.” .
The Messenger of Allah, may Allah bless him and grant him peace, arranged for Muadh ibn Jabal to call to the laws of Islam on the basis of his acknowledgment of monotheism. He said to him when he sent him to Yemen: "إنك تأتي قوما من أهل الكتاب فليكن أول ما تدعوهم إليه شهادة أن لا إله إلا الله وأن محمداً رسول الله، فإن هم أطاعوك لذلك فأعلمهم أن الله "افترض عليهم خمس صلوات في اليوم والليلة(narrated by Muslim) “You are going to a people of the People of the Book, so let the first thing you call them to be the testimony that there is no Allah but Allah and that Muhammad is the Messenger of Allah. If they obey you in that, then inform them that Allah has imposed on them five prayers during the day and night” .