Swiftest horse cannot overtake the word once spoken

Similar sayings:

Four things come not back: the spoken word, the sped arrow, the past life and the neglected opportunity. Four things come not back: the spoken word, the sped arrow, the past life and the neglected opportunity.
Slow in word, swift in deed Slow in word, swift in deed
Four horses cannot overtake the tongue Four horses cannot overtake the tongue
Many books do not use up words; many words do not use up thoughts Many books do not use up words; many words do not use up thoughts
If what we see is doubtful, how can we believe what is spoken behind the back If what we see is doubtful, how can we believe what is spoken behind the back

Chinese sayings and proverbs