Explanation:
Hazrat Khadijah (RA), the first wife of Prophet Muhammad (PBUH), passed away in the 10th year of Prophethood (around 619 CE). The same year also witnessed the death of Hazrat Abu Talib, the Prophet's uncle and protector. Due to these two great losses, that year became known as the "Aam al-Huzn" (Year of Sorrow).
After the death of Hazrat Khadijah (RA), the Prophet ﷺ continued preaching Islam in Makkah despite increasing persecution. Finally, the Prophet ﷺ migrated to Madinah in 622 CE.