When a man is sent to another man for some reasonand he does not tell him what it is

Al-Adab Al-Mufrad · Book 47 · Hadith 1156

حَدَّثَنَا مُحَمَّدٌ، قَالَ‏:‏ أَخْبَرَنَا عَبْدُ اللهِ بْنُ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِيهِ، عَنْ جَدِّهِ قَالَ‏:‏ قَالَ لِي عُمَرُ‏:‏ إِذَا أَرْسَلْتُكَ إِلَى رَجُلٍ، فَلاَ تُخْبِرْهُ بِمَا أَرْسَلْتُكَ إِلَيْهِ، فَإِنَّ الشَّيْطَانَ يُعِدُّ لَهُ كِذْبَةً عِنْدَ ذَلِكَ‏.‏

Aslam said, "'Umar said to me, 'If I send you to a man, do not tell him why I sent you to him. If you do, Shaytan will prepare a lie for him in that.'"