In narrations, more emphasis has been placed upon doing good to mothers; there are at least three reasons for this: first, mothers go through more hardships in raising the children, Second, the feeling of need for affection is higher in mothers, and the third reason is that most mothers are likely to be defenseless and more likely to be insecure and mistreated. Imam Sadiq (peace be upon him) says: a man came to Prophet (pbuh&hp) and said: O the messenger of Allah! Who should I do good to? The messenger of Allah said: do good to your mother. The man asked again: who else should I do good to? His eminence said: do good to your mother, the man asked: who else? The prophet said: do good to your mother. The man again asked who else should I do good to? The messenger of Allah said: do good to your father."
source : erfan.ir