Riyad as-Salihin 1029
Abu Hurairah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) went to the (Baqi') cemetery and said, "May you be secured from punishment, O dwellers of abode of the believers! We, if Allah wills, will follow you. I wish we see my brothers." The Companions said, "O Messenger of Allah! Are not we your brothers?" He (ﷺ) said, "You are my Companions, but my brothers are those who have not come into the world yet." They said; "O Messenger of Allah! How will you recognize those of your Ummah who are not born yet?" He (ﷺ) said, "Say, if a man has white-footed horses with white foreheads among horses which are pure black, will he not recognize his own horses?" They said; "Certainly, O Messenger of Allah!" He (ﷺ) said, "They (my followers) will come with bright faces and white limbs because of Wudu'; and I will arrive at the Haud (Al-Kauthar) ahead of them." [Muslim] .
وعنه أن رسول الله صلى الله عليه وسلم أتى المقبرة فقال‏:‏ ‏"‏السلام عليكم دار قوم مؤمنين وإنا إن شاء الله بكم لاحقون، وددت أنا قد رأينا إخواننا‏"‏ قالوا‏:‏ أولسنا إخوانك يا رسول الله‏؟‏ قال‏:‏ ‏"‏أنتم أصحابي، وإخواننا الذين لم يأتوا بعد‏"‏ قالوا‏:‏ كيف تعرف من لم يأتِ بعد من أمتك يا رسول الله‏؟‏ فقال‏:‏ ‏"‏أرأيت لو أن رجلا له خيل غر محجلة بين ظهري خيل دهم بهم، ألا يعرف خيله ‏؟‏‏"‏ قالوا بلى يا رسول الله، قال‏:‏ فإنهم يأتون غرًا محجلين من الوضوء وأنا فرطهم على الحوض ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏