Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: The Prophet (peace and blessings be upon him) said: "The best of you are those whose shoulders are softest in prayer, and no step carries a greater reward than the step a man takes in order to fill an empty space in the row."
Al-Tabarani recorded it in al-Mu'jam al-Awsat as it is mentioned here. Al-Bazzar also recorded it, but he did not record the words from "and no step" to the end. Al-Bazzar's chain is hasan (good), and al-Tabarani's chain contains a narrator, Layth bin Hammad, whom al-Daraqutni (may Allah have mercy on him) declared da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2501
Hadith Gradingمحدثین:إسنادہ حسن
Hadith Takhrij«أخرجه المعجم الأوسط للطبراني برقم: 5213، 5236»