Musnad Ahmad 1153:2324

Ya'qub narrated to us, he said: 'Abd al-'Aziz ibn al-Muttalib narrated to us, from Musa ibn 'Uqbah, from Abu Salamah ibn 'Abd al-Rahman, from 'Aishah, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Follow the right course, seek to be near perfection, and know that none of you will enter Paradise by his deeds." They said: "Not even you, O Messenger of Allah?" He said: "Not even me, unless Allah covers me with mercy from Him." And know that the most beloved of deeds to Allah are those that are most constant, even if they are few.