It is narrated from Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Nothing makes a servant's scale heavier than an animal on which he spends in the path of Allah, or on which (someone) is mounted in the path of Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17253