Full Sharh — Riyad as-Salihin 603
وعن ابن عباس رضي الله عنهما أن النبي صلى الله عليه وسلم لقي ركبا بالروحاء فقال: "من القوم؟" قالوا: المسلمون. قالوا من أنت؟ قال: "رسول الله" فرفعت امرأة صبيًا فقالت: ألهذا حج؟ قال "نعم ولك أجر" ((رواه مسلم)).
English Translation
Ibn 'Abbas (May Allah be pleased with them) reported:: The Prophet (ﷺ) came across a caravan at Ar-Rauha' and asked who the people in the caravan were. They replied that they were Muslims. They asked: "Who are you?" He (ﷺ) said, "I am the Messenger of Allah." Then a woman lifted up a boy to him and asked: "Would this child be credited with having performed the Hajj (pilgrimage)?" Whereupon he (ﷺ) said, "Yes, and you will have a reward.".
Source
Riyad as-Salihin(رياض الصالحين)
The Book of Hajj
Hadith Number
603