Allaah’s Aid is sought! If you said ‘Bismillaah’ it is sufficient, and if you said ‘Bismillaah ar-Rahmaan ar-Raheem’ then that is not a problem, because the Prophet sallAllaahu ‘alayhi wa sallam said: “O young boy mention the Name of Allaah”, and he did not say: ‘do not say ar-Rahmaan ar-Raheem’. So if you said ‘Bismillaah’ it is sufficient, and if you said ‘Bismillaah ar-Rahmaan ar-Raheem’ then that is not a problem. The Sharee’ah has within it, in a lot of the affairs scope for leeway. The people were with the Messenger of Allaah sallAllaahu ‘alayhi wa sallam on the farewell Hajj, some of them were pronouncing the Talbiyyah and some of them were pronouncing the Takbeer, and he did not say to the one making Takbeer ‘do not make Takbeer’, or to the one making the Talbiyyah ‘do not make the Talbiyyah’. And this affair is expansive. Ibn ‘Umar may Allaah be pleased with him, was from the most ardent of people upon following the Sunnah, and (even) with this he expanded upon the Talbiyyah and he said:
áÈíß Çááåã áÈíß¡ áÈíß áÇ ÔÑíß áß áÈíß¡ Åä ÇáÍãÏ æÇáäÚãÉ áß æÇáãáß áÇ ÔÑíß áß¡ áÈíß æ ÓÚÏíß¡ æÇáÎíÑ Ýí íÏíß¡ æÇáÑÛÈÇÁ Åáíß æÇáÚãá.
And none from amongst the Companions forbade him from that, from what we know. Because the affair (here) is expansive, except for the one who supplicates with a supplication that is not pertinent, or supplicates with something that is Haraam, so that is refuted regardless.
 Reported by al-Bukhaari (nos. 5376, 5377) in the Book of Foods and Muslim (no.2022) in the Book of Drinks.