Sayyiduna Abu al-Darda' (may Allah be pleased with him) narrates: I heard the Prophet (peace and blessings be upon him) say: "Whoever conveys to a ruler the need of someone who is unable to convey it (to the ruler) himself, Allah Almighty will keep both feet of that (person who conveyed the need) firm on the Sirat bridge at the time when feet will be slipping."
Al-Bazzar mentioned it within a long hadith; its chain contains Sa'id al-Barrad, and the rest of its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الخلافة / 9064