It does not matter if he said those exact words.
Those words reflect the spirituality of St. Francis.
The Rule and life of the Friars Minor is this, namely, to observe the Holy Gospel of our Lord Jesus Christ, by living …]
Preach the Gospel by observance, then, and by works.
Only much later down the Rule does St. Francis speak of preaching, and in very delicate words:
The friars are forbidden to preach in any diocese if the bishop objects to it.
No friar should dare to preach to the people unless he has been examined and approved by the Minister General of the Order and has received from him the commission to preach.
Moreover, I advise and admonish the friars that in their preaching, their words should be examined and chaste. They should aim only at the advantage and spiritual good of their listeners, telling them briefly about vice and virtue, punishment and glory, because our Lord himself kept his words short on earth.
“and when necessary, use words”.
St. Bonaventure called St. Francis a “Mirror of Perfection”, because he reflected Christ, who is Perfection, and who IS the Word of God, and thus preached the Good News by His very life, and only when necessary used words.
The high priest stood up and came forward and questioned Jesus, saying, “Do You not answer?” But Jesus remained silent.
Then Pilate questioned Him again, saying, “Do You not answer?” But Jesus still answered nothing.
[Herod] questioned him in many words. But he answered him nothing.