Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "A goat passed in front of the Messenger of Allah (peace and blessings be upon him) while he (peace and blessings be upon him) was in prayer, between him and the qiblah, and he (peace and blessings be upon him) did not break off his prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12362