One of the most popular quotes attributed to St. Francis of Assisi has a few variations.
Preach the Gospel at all times, use words if necessary.
Always preach the Gospel, if necessary, use words.
Even Pope Francis has attributed this quote to St. Francis of Assisi when addressing catechists in 2013, explaining the general "spirit" of the quotation:
We help, we lead others to Jesus with our words and our lives, with our witness. I like to recall what St. Francis of Assisi used to say to his friars: “Preach the Gospel at all times; if necessary, use words”. Words come… but witness comes first: people should see the Gospel, read the Gospel, in our lives.
Did St. Francis say these words?
Technically speaking, St. Francis of Assisi never spoke that exact quote. The words are similar to something he wrote in his Rule of 1221:
No brother may preach contrary to the forms and institutions of the holy church and unless it has been conceded to him by his minister. The minister must beware not to grant this concession to anyone indiscriminately. All the brothers, however, should preach by their actions.
This section is specifically addressed to "Preachers."
St. Francis was highly in favor of preaching and he preached countless times, often preaching to the birds and animals when nobody else would listen!
What St. Francis would agree with is that we need to preach with words and deeds.
We shouldn't be hypocrites, as Jesus instructs his apostles:
“The scribes and the Pharisees sit on Moses’ seat; so practice and observe whatever they tell you, but not what they do; for they preach, but do not practice. They bind heavy burdens, hard to bear, and lay them on men’s shoulders; but they themselves will not move them with their finger."
Our life needs to be a unified whole and our actions need to match the words we speak.