Shama-il Tirmidhi Chapter 39, Hadith Number 22 (269).

Ibn ‘Umar Radiyallahu ‘Anhu says: “I memorised from Rasulullah Sallallahu ‘Alayhi Wasallam eight raka-aat; two before zuhr and two after zuhr; two rak’ahs after maghrib and two after ‘eshaa”. Ibn ‘Urnar Radiyallahu’Anhu said.. “Hafsah related to me about the two rak’ahs of the morning, which I did not observe from Rasulullah Sallallahu’Alayhi Wasallam”.

Commentary
Since these two rak’ahs were almost always performed in the house and mostly at the time of fajr the mind is not attentive, therefore, it is not impossible for Sayyidina Ibn ‘Umar Radiyallahu ‘Anhu to say this. Some ‘ulama are of the opinion that the meaning of ‘not observing it’, is that he had not seen it at the time Sayyiditina Hafsah Radiyallahu ‘Anha had seen it. He had the opportunity of observing it later as we find in a few narrations, where Sayyidina Ibn’Umar Radiyallahu ‘Anhu describes his observance of these sunan. Of all the sunan, the one of the fajr is the most emphasised. Sayyidina Rasulullah Sallallahu ‘Alayhi Wasallam many a time emphasised its importance. For this reason some ‘ulama have declared it waajib. Particular importance should therefore be attached to it.