Allah says to His Messenger Muhammad ,
قُلْ
(Say) to these idolators who reject your message to them,
إِنَّمَآ أَنَاْ بَشَرٌ مِّثْلُكُمْ
(`I am only a man like you.) Whoever claims that I am lying, let him bring something like this that I have brought. For I did not know the Unseen, the matters of the past which you asked me about and I told you about, the story of the people of the Cave and of Dhul-Qarnayn, stories which are true -- I did not know any of this except for what Allah made known to me. And I tell you,
إِنَّمَآ إِلَـهُكُمُ
(that your God), Who calls you to worship Him,
إِلَـهٌ وَحِدٌ
(is One God), with no partner or associate.'
فَمَن كَانَ يَرْجُو لِقَآءَ رَبِّهِ
(So whoever hopes for the meeting with his Lord,) i.e., hopes for a good reward and recompense,
فَلْيَعْمَلْ عَمَلاً صَـلِحاً
(let him work righteousness) meaning, in accordance with the prescribed laws of Allah,
وَلاَ يُشْرِكْ بِعِبَادَةِ رَبِّهِ أَحَدَا
(and associate none as a partner in the worship of his Lord.) This is what is meant by seeking the pleasure of Allah alone with no associate or partner. These are the two basic features of acceptable deeds: their intent is for the sake of Allah alone, and are done in accordance with the way of the Messenger of Allah ﷺ. Imam Ahmad recorded that Mahmud bin Labid said that the Messenger of Allah ﷺ said:
«إِنَّ أَخْوَفَ مَا أَخَافَ عَلَيْكُمُ الشِّرْكُ الْأَصْغَر»
(What I fear the most for you is the small Shirk.) "They said: What is the small Shirk, O Messenger of Allah" He said,
«الرِّيَاءُ، يَقُولُ اللهُ يَوْمَ الْقِيَامَةِ إِذَا جَزَىَ النَّاسَ بِأَعْمَالِهِمْ: اذْهَبُوا إِلَى الَّذِينَ كُنْتُمْ تُرَاءُونَ فِي الدُّنْيَا، فَانْظُرُوا هَلْ تَجِدُونَ عِنْدَهُمْ جَزَاءً؟»
(Showing off (Ar-Riya'). Allah will say on the Day of Resurrection, when the people are rewarded or punished for their deeds, "Go to the one for whom you were showing off in the world and see if you will find any reward with him.") Imam Ahmad recorded that Abu Sa`id bin Abi Fadalah Al-Ansari, who was one of the Companions, said: "I heard the Messenger of Allah ﷺ say,
«إِذَا جَمَعَ اللهُ الْأَوَّلِينَ وَالْآخِرِينَ لِيَوْمِ الْقِيَامَةِ لِيَوْمٍ لَا رَيْبَ فِيهِ نَادَى مُنَادٍ: مَنْ كَانَ أَشْرَكَ فِي عَمَلٍ عَمِلَهُ للهِ أَحَدًا فَلْيَطْلُبْ ثَوَابَهُ مِنْ عِنْدِ غَيْرِ اللهِ،فَإِنَّ اللهَ أَغْنَى الشُّرَكَاءِ عَنِ الشِّرْك»
(Allah will gather the first and the last on the Day of Resurrection, the Day concerning which there is no doubt. A voice will call out, "Whoever used to associate anyone with Allah in the deeds which he did, let him seek his reward from someone other than Allah, for Allah is the least in need of any partner or associate.) It was also recorded by At-Tirmidhi and Ibn Majah. This is the end of the Tafsir of Surat Al-Kahf. Praise be to Allah, the Lord of all that exists.