The Prophet (peace and blessings be upon him) said:
"When a man says something and then looks around (to see that no one is listening), it is a trust (with the one who heard it)."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 486
Hadith Gradingالألبانی:حسن
Hadith Takhrijحم د ت الضياء عن جابر [ع] عن أنس. الصحيحة ١٠٩٠: الطحاوي.