It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he said: "When there are three persons (for the prayer), one of them should step forward as imam and the other two should stand in a row behind him."
He also said: "Once I came (to join the prayer) and stood on his left, so he (took hold of me and) made me stand on his right."
This narration is sahih (authentic) and mawquf.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الصلاة / 390
Hadith Gradingمحدثین:إسناده صحيح، موقوف
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :قال ابن حجر: صَحِيحٌ مَوْقُوفٌ . » «أورده ابن حجر فى "المطالب العالية"، 390، وأخرجه ابن أبى شيبة فى «مصنفه» برقم: 4974»