Tafsir of Al-Qalam 68:21

فَتَنَادَوْا مُصْبِحِينَ (So, they called out each other as the morning broke 68:21). This means that they starting waking up each other in the early morning that they should set out early if they wanted to harvest.

وَهُمْ يَتَخَافَتُونَ (...while they were whispering to each other ... 68:23). They were speaking in a low voice, lest a poor man should hear their talk and accompany them.