Tafsir Al-Jalalayn: Taa-Haa, Ayah 1

And from his narration on the authority of Ibn 'Abbas that he said upon the explanation of Allah's saying: (Ta. Ha. We have not revealed unto thee (Muhammad) this Qur'an that thou shouldst be distressed) We have not revealed the Qur'an to you that you should toil. This verse was revealed when the Prophet (pbuh) used to stand in prayer at night vigil until his feet swelled up, and so Allah alleviated this for him through this verse. He said: Taha, which in the dialect of Mecca means: O man, i.e. O Muhammad, We have not sent Gabriel with the Qur'an for you to toil.