Endless is Allah's Knowledge

Say, "If the sea were ink for [writing] the words of my Lord, the sea would be exhausted before the words of my Lord were exhausted, even if We brought the like of it as a supplement."18:109

Say: ‘If the sea, in other words, [if] its waters, were ink (midād is what one writes with) for the Words of my Lord, [Words] that testify to His laws and His marvels, such that these [Words] are written with it, the sea would be spent, in recording them, before the Words of my Lord were spent (read as tanfada or yanfada) even though We brought the like of it, namely, [the like of] the sea, as replenishment’, in order to add it to the other [sea], it would [also] be spent, while they [God’s Words] would not be exhausted (madadan, ‘as replenishment’, in the accusative because it is a specification).Tafsir al-Jalalayn

(Say) O Muhammad to the Jews: (Though the sea became ink for the Words of my Lord) for the knowledge of my Lord, (verily the sea would be used up before the Words of my Lord were exhausted) it is also said that 'the Words of my Lord' means: the disposition of my Lord, (even though We brought the like thereof to help) as an addition.Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs

The Words of the Lord can never be finished

Allah says: `Say, O Muhammad, if the water of the sea were ink for a pen to write down the words, wisdom and signs of Allah, the sea would run dry before it all could be written down.

[وَلَوْ جِئْنَا بِمِثْلِهِ]

(even if We brought like it) means, another sea, then another, and so on, additional seas to be used for writing. The Words of Allah would still never run out. As Allah says:

[وَلَوْ أَنَّمَا فِى الاٌّرْضِ مِن شَجَرَةٍ أَقْلاَمٌ وَالْبَحْرُ يَمُدُّهُ مِن بَعْدِهِ سَبْعَةُ أَبْحُرٍ مَّا نَفِدَتْ كَلِمَـتُ اللَّهِ إِنَّ اللَّهَ عَزِيزٌ حَكِيمٌ ]

(And if all the trees on the earth were pens and the sea (were ink), with seven seas behind it to increase it, yet the Words of Allah would not be exhausted. Verily, Allah is All-Mighty, All-Wise.) [31:27] Ar-Rabi` bin Anas said, "The parable of the knowledge of all of mankind, in comparison to the knowledge of Allah, is that of a drop of water in comparison to all of the oceans.'' Allah revealed that:

[قُل لَّوْ كَانَ الْبَحْرُ مِدَاداً لِّكَلِمَـتِ رَبِّى لَنَفِدَ الْبَحْرُ قَبْلَ أَن تَنفَدَ كَلِمَـتُ رَبِّى]

(Say: "If the sea were ink for the Words of my Lord, surely, the sea would be exhausted before the Words of my Lord would be finished,) Allah says that even if those oceans were ink for the Words of Allah, and all the trees were pens, the pens would be broken and the water of the sea would run dry, and the Words of Allah would remain, for nothing can outlast them. For no one can comprehend the greatness of Allah or praise Him as He deserves to be praised, except the One Who praises Himself. Our Lord is as He says He is and He is beyond what we can say. The blessings of this world, the beginning and end of it, in comparison to the blessings of the Hereafter, are like a mustard seed compared to the entire world.Tafsir Ibn Kathir