In same year 622AD,when the prophet recieved God  sanction for the hijira,he commended  his follower to migrate to madina in small numbers.
The quraysh in other side realized the plan of muhammad.Abu jahl suggested and his suggestion was agreed that strong man should be chosen from each tribe and all of them should strike  a sword on muhammad at once.
When muhammad heard about  their plant,he went out togather with Abubakar,his close friend to madina.The warrious,when they came to attack muhammad in his house,were found Ali Ibn Abi Talib alone instead of muhammad (s.a.w).