God has decreed that you worship none but Him, and (that you show) kindness to your parents. If one of them or both of them were to attain old age with you, say not a word of disrespect to them, nor repulse them, but speak to them a gracious word. And lower to them the wing of submission and humility through mercy, and say: My Rabb! Have Mercy on them both, as they did care for me when I was small

God has decreed that you worship none but Him, and (that you show) kindness to your parents. If one of them or both of them were to attain old age with you, say not a word of disrespect to them, nor repulse them, but speak to them a gracious word. And lower to them the wing of submission and humility through mercy, and say: My Rabb! Have Mercy on them both, as they did care for me when I was small

Reference:  http://muntakhabahadith.com