Sūrah No. 93. Revealed in Makkah, 11 verses. This Sūrah was revealed after a period in which there had been no revelation, and the enemies taunted the Prophet a about it. The Prophet a was anxiously waiting for revelation and these verses soothed his anxiety.
Many narrations say this sūrah and the sūrah that follows (Sūrat al-Inshirah) are one sūrah, and thus would have to be recited together in salāt after Sūrat al-Fatiha.