All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The wife’s sleep may or may not be a legitimate excuse for abstention from sexual intercourse with her husband. If her sleep is caused by previous fatigue, tiredness or illness, or her sleep is so deep that waking her up may expose her to hardship, in those cases, sleep will be considered a legitimate excuse. But if she entertains no great difficulty or trouble because of that, it will not be considered a legitimate excuse.
On the other hand, it is due on the husband to be kind and merciful, and choose, for fulfilling his sexual desire, the suitable time when both he and his wife are active. It is better to precede sexual intercourse with foreplay which adorns the desire and pushes away sleep, and not put her through difficulty in order to take his right. It is also due on the wife to submit to her husband as much as lies within her capacity.
Allaah Knows best.