SB 11.18.16
drsti-putam nyaset padam
vastra-putam pibej jalam
satya-putam vaded vacam
manah-putam samacaret
Translation:
A saintly person should step or place his foot on the ground only after verifying with his eyes that there are no living creatures, such as insects, who might be injured by his foot. He should drink water only after filtering it through a portion of his cloth, and he should speak only words that possess the purity of truth. Similarly, he should perform only those activities his mind has carefully ascertained to be pure.
Purport:
While walking, a saintly person is careful not to kill any tiny creatures on the ground. Similarly, he filters his drinking water through cloth to avoid swallowing small creatures living within the water. Speaking untruths simply for sense gratification is detrimental to devotional service and should be avoided. Speaking impersonal philosophy and glorifying the sense gratification of the material world, even that found in heavenly planets, contaminates the heart and must be avoided by those desiring perfection in the loving service of the Lord. By serious consideration one can understand that any activity other than devotional service to Lord Krsna has no ultimate value; therefore one should exclusively engage in the purified activities of Krsna consciousness.