(a) It is reported from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that he feared it might count as speech, that is, blowing in prayer.
(b) Imam al-Bayhaqi (may Allah have mercy on him) says: Blowing by itself is not speech, unless some speech that forms a word becomes apparent from it. If nothing intelligible is understood from it, then it is not speech.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3364