Question:
There is a hadith which says that a man asked the Prophetﷺ to tell him a deed that would lead him to Paradise. The Prophetﷺ said to fast, because nothing equals it. Another part says that fasting and the Qur’an will intercede. Fasting will say: “I prevented him from food and desires,” and the Qur’an will say: “I prevented him from sleep at night.” Their intercession will be accepted.
Is such a hadith authentic?
Answer:
Yes, such narrations exist.
One narration from Abdullah ibn Amr appears in Musnad Ahmad (6626). It states that fasting and the Qur’an will intercede for a servant on the Day of Judgment.
Fasting will say: “O my Lord, I prevented him from food and desires during the day. Accept my intercession for him.”
The Qur’an will say: “I prevented him from sleep during the night. Accept my intercession for him.”
Then their intercession will be accepted. However the version you mentioned combines two separate hadiths into one.
One hadith says fasting has no equal. Another hadith says the Qur’an and fasting will intercede. The narration about fasting and Qur’an intercession has two weak transmitters in its chain: Huyy ibn Abdullah and Ibn Lahi‘a. Both are considered weak by hadith scholars.
Because of those weak narrators, that particular narration about intercession is not considered strong.
But the hadith advising fasting as a deed that leads to Paradise is authentic. The Prophetﷺ emphasized fasting as an excellent act of worship.