Sunan an-Nasa'i 3859
It was narrated from Hammad -Ibn Abi Sulaiman- that he was asked about a man who hired a worker in return for food and he said:
"No, not until he tells him (what his wages will be)."
أَخْبَرَنَا مُحَمَّدُ بْنُ حَاتِمٍ، قَالَ أَنْبَأَنَا حِبَّانُ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ جَرِيرِ بْنِ حَازِمٍ، عَنْ حَمَّادٍ، - هُوَ ابْنُ أَبِي سُلَيْمَانَ - أَنَّهُ سُئِلَ عَنْ رَجُلٍ، اسْتَأْجَرَ أَجِيرًا عَلَى طَعَامِهِ قَالَ لاَ حَتَّى تُعْلِمَهُ‏.‏‏