وَقَدْ يُحْذَفُ فِعْلُهُ؛ لِقِيَامِ قَرِينَةٍ جَوَازًا، كَقَوْلِكَ لِلْقَادِمِ: «خَيْرَ مَقْدَمٍ».
Translation: Its governing verb may optionally be omitted when context supplies an adequate clue; the example is a welcoming expression addressed to an arriving person.
A contextual clue (qarīna) makes the unspoken action recoverable: the listener has just arrived and is being welcomed.