Sayyiduna Qays bin Abi Sa'sa'ah (may Allah be pleased with him) said: O Messenger of Allah, in how many days should I complete the Qur'an? He (peace and blessings be upon him) said: "In fifteen days." He said: I find myself stronger than that. He (peace and blessings be upon him) said: "In one week." He said: I find myself stronger even than that. The narrator said: So he continued reciting it in that way for a long time, until he grew old and began binding a band over his eyes; then he went back to fifteen days and recited it in fifteen days, and he would say: If only I had accepted the first concession of the Messenger of Allah (peace and blessings be upon him)!
Hadith Referenceالمعجم الكبير للطبراني / باب القاف / 15968