For fear of committing shirk
Ahmad 4:403
اللّهُـمَّ إِنّـي أَعـوذُبِكَ أَنْ أُشْـرِكَ بِكَ وَأَنا أَعْـلَمْ، وَأَسْتَـغْفِرُكَ لِما لا أَعْـلَم
O Allah, I seek refuge in You lest I associate anything with You knowingly, and I seek Your forgiveness for what I know not.