‏الصلاة : Hadeeth No:1540 Abu Qatada (a Companion of the Prophet) reported Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: When any one of you enters the mosque, he should observe two rak'ahs (of Nafl prayer) before sitting....

‏الجهاد والسير‏ : Hadeeth No:4295 Sulaiman b. Buraida repotted on the authority of his father that when Allaah's Messenger (sallAllaahu alayhi wa sallam) sent an Amir with a detachment he called him and advised him. The rest of the hadith is the same....