The voice of Hala, Hazrat Khadija’s sister, resembled Khadija’s voice a lot. One day, a woman’s voice asked for permission to enter his presence. Hazrat Muhammad (pbuh), who heard the voice, was astonished and prayed silently,

“O Allah! I hope this woman, who has asked for permission, is Hala!”

Indeed, she was Hala, a reminiscence of Khadija.