How authentic is the Hadith: "Whoever learns the Qur’an while young, Allah will mingle it with his flesh and blood," and who narrated it?

The narration with the mentioned wording, "Whoever learns the Qur'an while he is young, Allah will mix it with his flesh and blood," was reported by Al-Bayhaqi and Al-Bukhari. Al-Bayhaqi also narrated it with another wording: "Whoever learns the Qur'an in his youth, the Qur'an will be mixed with his flesh and blood. And whoever learns it in his old age, and it slips away from him, let him not abandon it, for he will have his reward twice." Ka'b al-Ahbar mentioned that there is a confirmation of this meaning in the Torah.