Abu Dawud Book 2, Hadith Number 1242.

Chapter : A seventh view that imam should lead each section in one rakah severellay and they should not pray the second rakah by themselves.

Narated By Ibn ‘Abbas : Allah, the Exalted, prescribed prayer for you, through the tongue of the Prophet (PBUH), four rak’ahs while resident, two rak’ahs while travelling and one rak’ah in the time of danger.