Musnad Ahmad 1287:0

Narrated to us by Yahya ibn Sa’id, from Hisham, who said: My father narrated to me, from a woman of the Banu ‘Abd al-Ashhal, who said: The Messenger of Allah (ﷺ) came to us and said: "O women of the Banu ‘Abd al-Ashhal, are you not pleased that if one of you is pregnant by her husband, and he is pleased with her, she has the reward of one who fasts and prays in the way of Allah? And when the labor pains come upon her, the inhabitants of the heavens and the earth do not know what is hidden for her of the coolness of the eyes. And when she gives birth, not a single drop of her milk flows, nor does a single suckle occur, except that she has for every drop and every suckle a reward. And if she stays awake at night for the sake of her child, she has the reward of freeing seventy slaves for the sake of Allah."