Sahih al-Bukhari · The Book of Hiring

4- بَابُ إِذَا اسْتَأْجَرَ أَجِيرًا لِيَعْمَلَ لَهُ بَعْدَ ثَلاَثَةِ أَيَّامٍ أَوْ بَعْدَ شَهْرٍ أَوْ بَعْدَ سَنَةٍ جَازَ، وَهُمَا عَلَى شَرْطِهِمَا الَّذِي اشْتَرَطَاهُ إِذَا جَاءَ الأَجَلُ:

(4) Chapter. It is legal if somebody hires someone to work for him after three days, or after one month or after a year. When that period elapses they should carry out their contract.

1 hadith · references 2264–2264