Musannaf Ibn Abi Shayba 9:1204

Ibn ‘Uyaynah narrated to us, from al-Zuhri, from ‘Ubayd Allah ibn ‘Abd Allah, from his father, who said: Subay‘ah gave birth after the death of her husband by twenty [days], or a month, or something similar. Abu al-Sanabil ibn Ba‘kak passed by her and said, "You have adorned yourself for suitors! No, not until four months and ten [days] have passed for you." So she came to the Prophet, may Allah bless him and grant him peace, and mentioned that to him. He said, "You have become lawful for suitors."