Mahīśāsaka Vinaya
Bhikkhunī Vibhaṅga
Confession 151
Origin Story
At that time, the bhikkhunīs slept under the same cover as lay women and non-Buddhist female renunciates. They saw each other’s bodies, and and sexual desire arose in their minds. … “I now lay down a precept for the bhikkhunīs, as explained above. From now on, this precept should be recited thus:
Final Ruling
‘If a bhikkhunī sleeps under the same cover as a lay woman or a non-Buddhist female renunciate, it’s a pācittiya.’”
Explanations
The remainder is as explained above.
If she first has her own cover, and puts another layer of cover on top, the offense isn’t committed.