Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
If your mother is in need and poor and does not have what will suffice her, and you have extra money beyond your needs and the need of those you are responsible for, like the wife, small children who cannot suffice themselves with housing, clothing and food, then you have to spend on her, in this case, according to what will suffice her.
What we advise you is to send money to your mother, even a small amount with which you will please her, and Allah will recompense you. Imam Al-Nawawi (may Allah have mercy on him) said in Mughni al-Muhtaj: 'He has to spend on his parents and grandparents, and spend on children and grandchildren, even if their religion is different, on the condition that one should spend of what is in excess of his daily bread and of those of his family in a day.'
The scholars determined that the person who is able to gain his bread has to gain what he will spend on his relatives, and if he has land, he has to sell it in order to spend on the relatives.
Therefore, it becomes clear that it is obligatory to spend on your mother. So do not neglect this duty.
However, if you do not have enough money to spend on yourself, your wife and your small children for a whole day and night, then in this case the wife and small children come in priority then your mother.
Allah knows best.