Attributed to Francis of Assisi
«Preach the Gospel at all times and, if necessary, use words.»
Misattributed
Verdict
It is not in Francis of Assisi's work
It does not appear in his writings or in the medieval biographies. The closest authentic text is Earlier Rule 17:3, 'All the brothers, however, should preach by their deeds', which does not disparage words (the same rule regulates preaching).
Source: Esser, Kajetan, O.F.M. Die Opuscula des hl. Franziskus von Assisi. Neue textkritische Edition. Grottaferrata: Collegium S. Bonaventurae ad Claras Aquas, 1976 (Spicilegium Bonaventurianum 13); editio minor: Opuscula sancti patris Francisci Assisiensis, 1978 (Bibliotheca Franciscana Ascetica Medii Aevi 12).
What they did say
Verified words of Francis of Assisi
«Most High, all-powerful, good Lord, yours are the praises, the glory and the honour and all blessing.»
Cántico de las criaturas, v. 1 (Asís, Biblioteca del Sacro Convento, cód. 338)
«Praised be you, my Lord, through our Sister bodily Death, from whom no living man can escape.»
Cántico de las criaturas, estrofa de la muerte (1226)
«The Lord gave me, Brother Francis, thus to begin doing penance: for when I was in sins, it seemed too bitter for me to see lepers. And the Lord himself led me among them and I showed mercy to them.»
Testamento 1–2