Mourning in Islam

Mourning is Islam is acceptable but what some Muslims are practicing now a days is strictly prohibited in Islam. As it is normal to cry over the death of love ones but wailing, shrieking is not allowed.

With reference to the below mention Ahadees one can understand what is allowed and what not.
Prophet Muhammad, Peace be upon him, also said: «I detest a woman who cries out very loudly, or shaves her hair, or tears her clothes when a beloved one dies» (Reported by Bukhari & Muslim).
Prophet Muhammad, Peace be upon him, said: «He is not of us who beats his face, tears his clothes and bewails loudly when misfortune happens to him as was done before during the days of ignorance» (Reported by Bukhari & Muslim).

 

For women who lost his husband has orders in Islam that she should follow Eddat.
This period is called the Eddat/Edda (Waiting period) which is prescribed by Allah in the Qur’an:
{وَالَّذِينَ يُتَوَفَّوْنَ مِنكُمْ وَيَذَرُونَ أَزْوَاجًا يَتَرَبَّصْنَ بِأَنفُسِهِنَّ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ۖ فَإِذَا بَلَغْنَ أَجَلَهُنَّ فَلَا جُنَاحَ عَلَيْكُمْ فِيمَا فَعَلْنَ فِي أَنفُسِهِنَّ بِالْمَعْرُوفِ ۗ وَاللَّهُ بِمَا تَعْمَلُونَ خَبِيرٌ}
‘Translation’ {and those who are taken in death among you and leave wives behind – they, [the wives, shall] wait four months and ten [days]. And when they have fulfilled their term, then there is no blame upon you for what they do with themselves in an acceptable manner. And Allah is [fully] acquainted with what you do.} [Surah Al-Baqarah: 234].