Sunan Abi Dawud 43:276

The tradition mentioned above has also been transmitted by al-Bara b. Azil from the prophet (May peace be upon him) to the same effect through a different chain of narrators. One transmitter said:

when you go to your bed while you are in the state of purification. The other said: Perform ablution like the ablution for prayer. He then transmitted the tradition to the effect as Mu’tamir transmitted.