Doubtful Things and Whispers of Shaytaan (Ahadith 1767 – 1768)
Volume 3, Book 34, Number 272:
Narrated ‘Abbas bin Tamim:
that his uncle said: “The Prophet (sallallaahu `alayhi wasallam) was asked: If a person feels something during his prayer; should one interrupt his prayer?” The Prophet (sallallaahu `alayhi wasallam) said: No! You should not give it up unless you hear a sound or smell something.” Narrated Ibn Abi Hafsa: Az-Zuhri said, “There is no need of repeating ablution unless you detect a smell or hear a sound.”
Here, you don’t listen to such thoughts, because they’re whispers of Shaytaan who wants you to not concentrate on your Salah.
Volume 3, Book 34, Number 273:
Narrated ‘Aisha (radiallaahu `anhaa):
Some people said, “O Allah’s Apostle (sallallaahu `alayhi wasallam)! Meat is brought to us by some people and we are not sure whether the name of Allah has been mentioned on it or not (at the time of slaughtering the animals).” Allah’s Apostle (sallallaahu `alayhi wasallam) said (to them), “Mention the name of Allah and eat it.”
This is not a general principle. There’s background to it. Quoting IslamQA:
As for the claim that some make, that it is enough merely to mention the name of Allaah when eating, this was reported regarding some Muslims who were new in Islam. The Sahaabah (may Allaah be pleased with them) asked the Prophet (peace and blessings of Allaah be upon him) about this, saying, “O Messenger of Allaah, some people who are new in Islam brought us some meat, and we do not know whether they mentioned the name of Allaah over it or not.” The Prophet (peace and blessings of Allaah be upon him) said: “Say the name of Allaah over it and eat it.” (Reported by al-Bukhaari). The command should be understood as meaning that one should be on the safe side, provided that one does not know beforehand that the meat is not slaughtered properly. And Allaah knows best.