Muaza bint Abdullah Adawiya reported,

She asked Ayesha رضي الله عنها, "How many units did the Messenger of Allah ﷺ pray for the Duha prayer?"Ayesha replied, "Four units, and he would add as many as he wished."

Muslim 1663

Sahih

حدثنا شيبان بن فروخ حدثنا عبد الوارث حدثنا يزيد يعني الرشك

حدثتني معاذة

أنها سألت عائشة رضي الله عنها كم كان رسول الله ﷺ يصلي صلاة الضحى قالت أربع ركعات ويزيد ما شاء

مسلم 1663صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Travelers' prayer and its shortening
Chapter
Recommendation of Duha prayer, that its minimum is two rakahs and its most complete is eight rakahs and its middle is four or six rakahs, and the encouragement to maintain it
Numbering
Darussalam 1663
Muslim 1663