Abu Dawud Book 2, Hadith Number 1256.

Chapter : On lying after praying the two rakahs before the dawn prayer.

Narated By Abu Hurairah : The Prophet (PBUH) said: If any of you prays two rak’ahs before the dawn prayer, he should lie at his right side.

Marwan ibn al-Hakam said to him: Is it not enough that one of us walks to the mosque until he lies at his right side? According to the version of Ubaydullah, he (Abu Hurairah) replied: No.

This statement (of Abu Hurairah) reached Ibn Umar. He said: Abu Hurairah exceed limits on himself. He was asked: Do you look askance at what he says? He replied: No, but he dared and we showed cowardice. This (criticism of Ibn Umar) reached Abu Hurairah. He said: What is my sin if I remembered and they forgot?