The Quran

198

لَيسَ عَلَيكُم جُناحٌ أَن تَبتَغوا فَضلًا مِن رَبِّكُم ۚ فَإِذا أَفَضتُم مِن عَرَفاتٍ فَاذكُرُوا اللَّهَ عِندَ المَشعَرِ الحَرامِ ۖ وَاذكُروهُ كَما هَداكُم وَإِن كُنتُم مِن قَبلِهِ لَمِنَ الضّالّينَ

Muhammad Asad

[However,] you will be committing no sin if [during the pilgrimage] you seek to obtain any bounty from your Sustainer.¹ And when you surge downward in multitudes from 'Arafat,² remember God at the holy place, and remember Him as the One who guided you after you had indeed been lost on your way;³

I.e., by trading while in the state of ihram. Muhammad 'Abduh points out (in Manar II, 231) that the endeavour "to obtain any bounty from your Sustainer" implies God-consciousness and, therefore, constitutes a kind of worship-provided, of course, that this endeavour does not conflict with any other, more prominent religious requirement.
The gathering of all pilgrims on the plain of 'Arafat, east of Mecca, takes place on the 9th of Dhu'l-Hijjah and constitutes the climax of the pilgrimage. The pilgrims are required to remain until sunset on that plain, below the hillock known as Jabal ar-Rahmah ("the Mount of Grace") - a symbolic act meant to bring to mind that ultimate gathering on Resurrection Day, when every soul will await God's judgment. Immediately after sunset, the multitudes of pilgrims move back in the direction of Mecca, stopping overnight at a place called Muzdalifah, the "holy place" referred to in the next clause of this sentence.
Lit., "and remember Him as He has guided you, although before that you had indeed been among those who go astray".