Laylat al-Mabit (Arabic: لیلة المبیت), is the night in which the prophet of Islam started his emigration from Mecca to Medina. This day is taken place on the first of Rabi' al-awwal. Due to the decision of Quraysh to kill the prophet, 'Ali b. Abi Talib slept in his place and the prophet left Mecca. the verse 207 of Surat al-Baqarah is revealed in this regard to show the sacrifice of Imam 'Ali for saving the life of the prophet.
Verse of Laylat al-Mabit
According to Quran commentators, verse of 207 of Surat al-Baqarah is revealed in regard to Ali's risking his life in order to save Mohammad.
And of the people is he who sells himself, seeking means to the approval of Allah. And Allah is kind to [His] servants.
References
Laylat al-Mabit Wikipedia(Text) CC BY-SA