Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

 

The answer for your question is explicitly mentioned in the hadith of the Prophet (peace be upon him). Um Habiba narrated: The Prophet (peace be upon him) said, “It is not lawful for a Muslim woman who believes in Allah and the Last Day to mourn for more than three days, except for her husband, for whom she should mourn for four months and ten days.” (Al-Bukhari)

 

 

Almighty Allah knows best.