Is it considered a sin not to kiss the mother's hand while kissing the father's hand daily?

We pray that Allah grants the questioner success and increases his devotion to his parents. Justice requires kissing the mother's hand as well; indeed, the mother has a greater right to devotion than the father. Nevertheless, we hope that the questioner will not incur sin, as long as the mother is not affected by his not kissing her hand while he kisses the father's hand.