Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: Indeed, Allah Almighty and His angels send mercy upon those in the front rows. The narrator says: What is meant is the first row.
Al-Tabarani recorded it in al-Mu'jam al-Kabir as a mawquf report (a Companion's own statement), and its chain contains a narrator who has not been named.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2517