The Prophet Muhammad [sallallaahu alayhi wasallam] is reported to have said that the best behaviour on the passing of a family member is for one to practice Sabr (patience with Allah's will) and to hope for Allah's reward, both in this world and in the life after death. Even when he heard of the serious illness of his own grandchild, the holy Prophet [sallallaahu alayhi wasallam] sent the following message to the mother of the child, his daughter Zaynad [radhiallaahu anhu]:

'Ultimately, everything belongs to Allah. Even when a child is in the lap of its mother, this child is Allah's property. And when Allah takes away the child from its parents, then also (remember that) it is His property. In Allah's plan, everything has a time-limit and this is unchangeable. So, it is best to practice Sabr and hope for Allah's reward.'

The following is a letter which the Holy Prophet [sallallaahu alayhi wasallam] wrote to a companion who had lost his son:

'In the name of Allah, the Giver of Mercy, the Merciful: from Muhammad the Messenger of Allah to the father. I give praise to Allah, for there is no God besides Him. Thereafter, (I pray) that Allah increase your reward greatly and that He inspire Sabr in you, and thankfulness in all of us - because we ourselves, our wealth, our relations and our children are the nicest gifts from Almighty Allah...

gifts that we enjoy for a limited period until He takes them away at an appointed time ... And your son was among the nicest gifts of Allah through whom you enjoyed pleasure and happiness. Allah's taking him away from you is in exchange for a big reward - the prayer, the quality of mercy and the guidance that He bestows upon you...' 

Finally, take note of the words of the messenger of Allah on the occasion of the death of his only son, Ibraahim:

'Our eyes are filled with tears, our hearts with grief, but we say nothing with our lips except that which pleases Allah.... Verily, to Allah we belong, and to Him we return.'
Courtesy: www.everymuslim.net