Is following the Sunnah better than performing a large amount of permissible deeds?

Question : We were told that following the Sunnah is better than increasing one's deeds. In the hadith of Aisha (may Allah be pleased with her), the Prophet (peace and blessings be upon him) said: Is one rak'ah better in reward and greater in reward than twenty-one rak'ahs?

Answer : Yes, we say it is better. But note that the Prophet's (peace and blessings be upon him) night prayer of eleven rak'ahs is equivalent to our prayer of three hundred rak'ahs, is it not? He would prolong the prayer until some of the Companions, who were young, were unable to keep up with him. So be mindful of this.