It is narrated from Sayyiduna Abdullah bin Zayd (may Allah be pleased with him): I heard the Messenger of Allah (peace and blessings be upon him) saying: "Indeed Allah, the Mighty and Majestic, and His angels send their special mercy upon those who keep the rows (of prayer) joined together, and the congregational prayer holds twenty-five times more virtue and reward than the prayer of a person alone."
Musnad Abi Ya'la, hadith no. 407. Its chain contains Musa bin Ubaydah al-Rabadhi, who is a da'if (weak) narrator; however, other authentic hadith are narrated about joining the rows and the virtue of congregational prayer.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الصلاة / 407
Hadith Gradingمحدثین:إسناده ضعيف جدًا، مرسل
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :مرسل، إسناده ضعيف جدًا. » «أخرجه المعجم الأوسط للطبراني برقم: 5063، وأخرجه مجمع الزوائد ومنبع الفوائد برقم: 2136»