...and if you try to count the blessings of Allah, never will you be able to count them... Surah Ibrahim
Allah states that the servants are never able to count His blessings, let alone thank Him duly for them. In Sahih Al-Bukhari it is recorded that the Messenger of Allah( Peace and blessings be upon him) used to supplicate:
O Allah ! All praise is due to You, without being able to sufficiently thank You, nor ever wish to be cutoff from You, nor ever feeling rich from relying on You; our Lord!
It was reported that Prophet Dawud peace be upon him, used to say in his supplication, "O Lord! How can I ever duly thank You, when my thanking You is also a favor from You to me''
Allah the Exalted answered him, "Now, you have thanked Me sufficiently, O Dawud,'' meaning, `when you admitted that you will never be able to duly thank Me.' (Tafsir Ibn Kathir)