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.