The student of Hadhrat Abdullaah bin Umar (RA), Hadhrat Mujaahid (A.R) says, "I performed salaah behind Hadhrat Abdullaah bin Umar (RA) and he never raised his hands except for the first Takbeer (Tahreema)." [Tahaawi, Vol.1 Pg.110 - the hadith is authentic].

Therefore, he never raised his hands when proceeding into Ruku. On the other hand, certain narrations report that Hadhrat Abdullaah bin Umar (RA) used to raise his hands when proceeding into Ruku. Haafidh Ibn Hajar Asqalaani (A.R) reconciles the two narrations by saying that Hadhrat Abdullaah bin Umar (RA) sometimes raised his hands and sometimes did not [Fat'hul Baari, Vol.4 Pg.140]. This proves that the Sahaaba (RA) did not regard this act to be an emphasised Sunnah. It was therefore not their constant practice.

Hadhrat Abdullaah bin Umar (RA) also said, "When any of you perform salaah behind an Imaam, the recitation of the Imaam is sufficient for him (i.e. he will not have to recite any Qiraa'ah himself). However, if he performs salaah on his own, he will have to recite." [Mu'atta Pg.107]

He also mentioned that the Maghrib salaah is the Witr salaah of the day. [Mu'atta of Imaam Maalik Pg.110] Therefore, like Maghrib, the Witr salaah will also comprise of three consecutive rakaahs with Tashahhud (sitting posture) after the first two.