Sahih Bukhari, Chapter: Jihaad (Fighting for the cause of Allah)

The Prophet (SAW) delivered a Khutba (sermon) and said, "Zaid took the flag and was martyred, and then Jafar took the flag and was martyred, and then Abdullah bin Rawaha took the flag and was martyred too, and then Khalid bin Al-Walid took the flag though he was not appointed as a commander and Allah made him victorious." The Prophet (SAW) further added, "It would not please us to have them with us." Aiyub, a sub-narrator, added, "Or the Prophet (SAW), shedding tears, said, 'It would not please them to be with us."